rts: Fallback to mmap when vm_allocate fails for Darwin 10 and later (fix #21049)
This MR modified the logic of my_mmap()
under rts/posix/OSMem.c
to allow newer Mac OS X/macOS to use mmap(2)
to perform allocations when vm_allocate
fails, this also prevented the program from aborting itself when vm_allocate
fails, to match the behavior where mmap
method fails (which was returning NULL).
This fixes haskell/ghcup-hs#384 and #21049