pyenv で python のインストールでエラーになる

Question

macOS 10.15.6(Catalina)にて、pyenv で

pyenv install 3.6.11

と入れると

python-build: use openssl@1.1 from homebrew
python-build: use readline from homebrew
Downloading Python-3.6.11.tar.xz...
-> https://www.python.org/ftp/python/3.6.11/Python-3.6.11.tar.xz
Installing Python-3.6.11...
python-build: use readline from homebrew
python-build: use zlib from xcode sdk

BUILD FAILED (OS X 10.15.6 using python-build 20180424)

Inspect or clean up the working tree at /var/folders/66/ggg5xl991933f9ctjtv78ync0000gn/T/python-build.20200914100109.18238
Results logged to /var/folders/66/ggg5xl991933f9ctjtv78ync0000gn/T/python-build.20200914100109.18238.log

Last 10 log lines:
 ^
216 warnings and 10 errors generated.
make: *** [Programs/python.o] Error 1
make: *** Waiting for unfinished jobs....
216 warnings and 10 errors generated.
216 warnings and 10 errors generated.
216 warnings and 10 errors generated.
make: *** [Parser/grammar1.o] Error 1
make: *** [Parser/listnode.o] Error 1
make: *** [Parser/acceler.o] Error 1

とエラーになってしまいます。
log を見ると最後の方で以下のような記載がありますが、どう対処していいのか分からない状態です。

In file included from Parser/listnode.c:4:
In file included from ./Include/pgenheaders.h:10:
In file included from In file included from Parser/acceler.c:13:
In file included from ./Include/pgenheaders.h:10:
In file included from ./Include/Python.h:36:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/unistd.h:72:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/unistd.h:202:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_gid_t.h:31:25: error: cannot combine with previous 'type-name' declaration specifier
typedef __darwin_gid_t  gid_t;
                        ^
./pyconfig.h:1513:15: note: expanded from macro 'gid_t'
#define gid_t int
              ^
In file included from Parser/acceler.c:13:
In file included from ./Include/pgenheaders.h:10:
In file included from ./Include/Python.h:36:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/unistd.h:72:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/unistd.h:202:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_gid_t.h:31:1: warning: typedef requires a name [-Wmissing-declarations]
typedef __darwin_gid_t  gid_t;
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./Include/Python.h:36:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/unistd.h:72:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/unistd.h:202:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_gid_t.h:31:25: error: cannot combine with previous 'type-name' declaration specifier
typedef __darwin_gid_t  gid_t;
                        ^
./pyconfig.h:1513:15: note: expanded from macro 'gid_t'
#define gid_t int
              ^
In file included from Parser/listnode.c:4:
In file included from ./Include/pgenheaders.h:10:
In file included from ./Include/Python.h:36:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/unistd.h:72:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/unistd.h:202:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_gid_t.h:31:1: warning: typedef requires a name [-Wmissing-declarations]
typedef __darwin_gid_t  gid_t;
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from Parser/grammar1.c:4:
In file included from ./Include/Python.h:53:
In file included from ./Include/pyport.h:205:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/time.h:184:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/time.h:69:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_clock_t.h:31:33: error: 'long type-name' is invalid
typedef __darwin_clock_t        clock_t;
                                ^
./pyconfig.h:1507:17: note: expanded from macro 'clock_t'
#define clock_t long
                ^
In file included from Parser/grammar1.c:4:
In file included from ./Include/Python.h:53:
In file included from ./Include/pyport.h:205:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/time.h:184:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/time.h:69:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_clock_t.h:31:1: warning: typedef requires a name [-Wmissing-declarations]
typedef __darwin_clock_t        clock_t;
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from ./Programs/python.c:3:
In file included from ./Include/Python.h:89:
./Include/unicodeobject.h:68:2: error: Must define SIZEOF_WCHAR_T
#error Must define SIZEOF_WCHAR_T
 ^
In file included from Parser/acceler.c:13:
In file included from ./Include/pgenheaders.h:10:
In file included from ./Include/Python.h:53:
In file included from ./Include/pyport.h:205:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/time.h:184:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/time.h:69:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_clock_t.h:31:33: error: 'long type-name' is invalid
typedef __darwin_clock_t        clock_t;
                                ^
./pyconfig.h:1507:17: note: expanded from macro 'clock_t'
#define clock_t long
                ^
In file included from Parser/acceler.c:13:
In file included from ./Include/pgenheaders.h:10:
In file included from ./Include/Python.h:53:
In file included from ./Include/pyport.h:205:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/time.h:184:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/time.h:69:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_clock_t.h:31:1: warning: typedef requires a name [-Wmissing-declarations]
typedef __darwin_clock_t        clock_t;
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from Parser/listnode.c:4:
In file included from ./Include/pgenheaders.h:10:
In file included from ./Include/Python.h:53:
In file included from ./Include/pyport.h:205:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/time.h:184:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/time.h:69:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_clock_t.h:31:33: error: 'long type-name' is invalid
typedef __darwin_clock_t        clock_t;
                                ^
./pyconfig.h:1507:17: note: expanded from macro 'clock_t'
#define clock_t long
                ^
In file included from Parser/listnode.c:4:
In file included from ./Include/pgenheaders.h:10:
In file included from ./Include/Python.h:53:
In file included from ./Include/pyport.h:205:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/time.h:184:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/time.h:69:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_clock_t.h:31:1: warning: typedef requires a name [-Wmissing-declarations]
typedef __darwin_clock_t        clock_t;
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from Parser/grammar1.c:4:
In file included from ./Include/Python.h:89:
./Include/unicodeobject.h:68:2: error: Must define SIZEOF_WCHAR_T
#error Must define SIZEOF_WCHAR_T
 ^
In file included from Parser/acceler.c:13:
In file included from ./Include/pgenheaders.h:10:
In file included from ./Include/Python.h:89:
./Include/unicodeobject.h:68:2: error: Must define SIZEOF_WCHAR_T
#error Must define SIZEOF_WCHAR_T
 ^
In file included from Parser/listnode.c:4:
In file included from ./Include/pgenheaders.h:10:
In file included from ./Include/Python.h:89:
./Include/unicodeobject.h:68:2: error: Must define SIZEOF_WCHAR_T
#error Must define SIZEOF_WCHAR_T
 ^
216 warnings and 10 errors generated.
make: *** [Programs/python.o] Error 1
make: *** Waiting for unfinished jobs....
216 warnings and 10 errors generated.
216 warnings and 10 errors generated.
216 warnings and 10 errors generated.
make: *** [Parser/grammar1.o] Error 1
make: *** [Parser/listnode.o] Error 1
make: *** [Parser/acceler.o] Error 1

pyenv の python インストール系で記事になっているものはいくつか試しました（エラーコードが異なるので、的外れだとは思いますが）。

• openssl: インストール済み（参考: openssl@1.1ならmacOS MojaveとpyenvでPython 3.7がインストール可能）
• Command Line Tool: 再インストール（参考: pyenv install でエラーが発生する）
• zlib:インストール済み（参考: pyenvでpythonのインストールがzlibエラーで失敗した時の対応）

Answer 1

clang が anaconda 経由のものと、xcode 経由ものが存在しており、本来であれば後者で実行すべきところを、前者で実行していたのが原因でした。
anadonda 環境を削除したところ上手く動きました。