cocoapodsがインストールできない

前提・実現したいこと

iosアプリを作ろうとプログラミングを始めましたが、教材で、まずcocoapodsをインストールする必要があると書いてありましたがインストールしようとしてもエラーが出てしまいます。どうしてでしょうか。

発生している問題・エラーメッセージ

Building native extensions. This could take a while...
ERROR: Error installing cocoapods:
ERROR: Failed to build gem native extension.

current directory: /Library/Ruby/Gems/2.6.0/gems/ffi-1.14.2/ext/ffi_c

/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/bin/ruby -I /Library/Ruby/Site/2.6.0 -r ./siteconf20210111-5060-17ongcv.rb extconf.rb
checking for ffi.h... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers. Check the mkmf.log file for more details. You may
need configuration options.

Provided configuration options:
--with-opt-dir
--without-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/bin/$(RUBY_BASE_NAME)
--with-ffi_c-dir
--without-ffi_c-dir
--with-ffi_c-include
--without-ffi_c-include=${ffi_c-dir}/include
--with-ffi_c-lib
--without-ffi_c-lib=${ffi_c-dir}/lib
--enable-system-libffi
--disable-system-libffi
--with-libffi-config
--without-libffi-config
--with-pkg-config
--without-pkg-config
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:467:in try_do': The compiler failed to generate an executable file. (RuntimeError) You have to install development tools first. from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:585:in block in try_compile'
from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:534:in with_werror' from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:585:in try_compile'
from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:1109:in block in have_header' from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:959:in block in checking_for'
from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:361:in block (2 levels) in postpone' from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:331:in open'
from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:361:in block in postpone' from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:331:in open'
from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:357:in postpone' from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:958:in checking_for'
from /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0/mkmf.rb:1108:in have_header' from extconf.rb:10:in system_libffi_usable?'
from extconf.rb:42:in `<main>'

To see why this extension failed to compile, please check the mkmf.log which can be found here:

/Library/Ruby/Gems/2.6.0/extensions/universal-darwin-19/2.6.0/ffi-1.14.2/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /Library/Ruby/Gems/2.6.0/gems/ffi-1.14.2 for inspection.
Results logged to /Library/Ruby/Gems/2.6.0/extensions/universal-darwin-19/2.6.0/ffi-1.14.2/gem_make.out