cmake HAVE_M_MMAP_THRESHOLD examples

alibaba/AliSQL storage/tokudb/ft-index/cmake_modules/TokuFeatureDetection.cmake :49 

check_symbol_exists(M_MMAP_THRESHOLD "malloc.h" HAVE_M_MMAP_THRESHOLD)

percona/PerconaFT cmake_modules/TokuFeatureDetection.cmake :50 

check_symbol_exists(M_MMAP_THRESHOLD "malloc.h" HAVE_M_MMAP_THRESHOLD)

oscarlab/betrfs cmake_modules/TokuFeatureDetection.cmake :54 

check_symbol_exists(M_MMAP_THRESHOLD "malloc.h" HAVE_M_MMAP_THRESHOLD)