cmake LIBCXX_HAS_C_LIB examples

PlatONnetwork/pWASM libc++/libcxx/cmake/config-ix.cmake :10 

check_library_exists(c fopen "" LIBCXX_HAS_C_LIB)

CTSRD-CHERI/cheribsd contrib/subrepo-cheri-libc++/cmake/config-ix.cmake :22 

check_library_exists(c fopen "" LIBCXX_HAS_C_LIB)