FLANN cmake error

MSYS2のMingw-w64であるアプリケーションをcmakeのコマンドでビルドしようとしています．しかし，以下のようなエラーが出ます．
-- Checking for module 'flann>=1.7.0'
-- No package 'flann' found
CMake Error at C:/msys64/mingw64/share/cmake-3.12/Modules/FindPackageHandleStandardArgs.cmake:137 (message):
Could NOT find FLANN (missing: FLANN_LIBRARY) (Required is at least version
"1.7.0")
Call Stack (most recent call first):
C:/msys64/mingw64/share/cmake-3.12/Modules/FindPackageHandleStandardArgs.cmake:378 (_FPHSA_FAILURE_MESSAGE)
cmake/Modules/FindFLANN.cmake:54 (find_package_handle_standard_args)
CMakeLists.txt:286 (find_package)

-- Configuring incomplete, errors occurred!
See also "C:/msys64/home/survey/pcl-master/build/CMakeFiles/CMakeOutput.log".
See also "C:/msys64/home/survey/pcl-master/build/CMakeFiles/CMakeError.log".

FLANNが見つからないというエラーですが，FLANNは別途，ビルド済みです．
FindFLANN.cmakeには，以下のように書かれています．このような場合，ビルド済みのFLANNをcmakeで見つけるには，どのようにしたらいいでしょうか？

if(FLANN_USE_STATIC)
set(FLANN_RELEASE_NAME flann_cpp_s)
set(FLANN_DEBUG_NAME flann_cpp_s-gd)
else(FLANN_USE_STATIC)
set(FLANN_RELEASE_NAME flann_cpp)
set(FLANN_DEBUG_NAME flann_cpp-gd)
endif(FLANN_USE_STATIC)

find_package(PkgConfig QUIET)
if (FLANN_FIND_VERSION)
pkg_check_modules(PC_FLANN flann>=${FLANN_FIND_VERSION})
else(FLANN_FIND_VERSION)
pkg_check_modules(PC_FLANN flann)
endif(FLANN_FIND_VERSION)

set(FLANN_DEFINITIONS ${PC_FLANN_CFLAGS_OTHER})

find_path(FLANN_INCLUDE_DIR flann/flann.hpp
HINTS ${PC_FLANN_INCLUDEDIR} ${PC_FLANN_INCLUDE_DIRS} "${FLANN_ROOT}" "$ENV{FLANN_ROOT}"
PATHS "$ENV{PROGRAMFILES}/Flann" "$ENV{PROGRAMW6432}/Flann"
PATH_SUFFIXES include)

find_library(FLANN_LIBRARY
NAMES ${FLANN_RELEASE_NAME}
HINTS ${PC_FLANN_LIBDIR} ${PC_FLANN_LIBRARY_DIRS} "${FLANN_ROOT}" "$ENV{FLANN_ROOT}"
PATHS "$ENV{PROGRAMFILES}/Flann" "$ENV{PROGRAMW6432}/Flann"
PATH_SUFFIXES lib)

find_library(FLANN_LIBRARY_DEBUG
NAMES ${FLANN_DEBUG_NAME} ${FLANN_RELEASE_NAME}
HINTS ${PC_FLANN_LIBDIR} ${PC_FLANN_LIBRARY_DIRS} "${FLANN_ROOT}" "$ENV{FLANN_ROOT}"
PATHS "$ENV{PROGRAMFILES}/Flann" "$ENV{PROGRAMW6432}/Flann"
PATH_SUFFIXES lib debug/lib)

if(NOT FLANN_LIBRARY_DEBUG)
set(FLANN_LIBRARY_DEBUG ${FLANN_LIBRARY})
endif(NOT FLANN_LIBRARY_DEBUG)

set(FLANN_INCLUDE_DIRS ${FLANN_INCLUDE_DIR})
set(FLANN_LIBRARIES optimized ${FLANN_LIBRARY} debug ${FLANN_LIBRARY_DEBUG})

include(FindPackageHandleStandardArgs)
find_package_handle_standard_args(FLANN DEFAULT_MSG FLANN_LIBRARY FLANN_INCLUDE_DIR)

mark_as_advanced(FLANN_LIBRARY FLANN_LIBRARY_DEBUG FLANN_INCLUDE_DIR)

if(FLANN_FOUND)
message(STATUS "FLANN found (include: ${FLANN_INCLUDE_DIRS}, lib: ${FLANN_LIBRARIES})")
if(FLANN_USE_STATIC)
add_definitions(-DFLANN_STATIC)
endif(FLANN_USE_STATIC)
endif(FLANN_FOUND)