[Chapel Merge] Add workaround to aligned_alloc() not being availa

Branch: refs/heads/master
Revision: 8fb73a9
Author: bradcray
Log Message:

Merge pull request #17849 from bradcray/address-aligned-alloc-osx

Add workaround to aligned_alloc() not being available on Mac OS X 10.14

[co-developed with @mppf]

aligned_alloc() doesn't seem to be available on Mac OS X 10.14 despite its claim for supporting C11, so this adds an #ifdef'd workaround using posix_memalign().

Modified Files:
M compiler/next/lib/util/my_aligned_alloc.c

Compare: https://github.com/chapel-lang/chapel/compare/69d5d1a77ce8...8fb73a9dcf80