Support darwin arm64 in fswatcher

[jdrews]

This PR enables the fswatcher package to run on darwin arm64 (such as Mac M1 silicon).

[jdrews]

Hmm looks like the appveyor build failed because of a cygheap failure. Looks like a CI problem and not related to this PR.
https://ci.appveyor.com/project/fstab/grok-exporter/builds/46875026#L416

C:\cygwin64\bin\bash -c "PATH='/usr/sbin:/usr/bin:/sbin:/bin' x86_64-w64-mingw32-objdump -p /cygdrive/c/go/bin/grok_exporter.exe | grep 'DLL Name:'"
0 [main] grep (3320) C:\Program Files\Git\usr\bin\grep.exe: *** fatal error - cygheap base mismatch detected - 0x800000000/0x210351408.
This problem is probably due to using incompatible versions of the cygwin DLL.
Search for cygwin1.dll using the Windows Start->Find/Search facility
and delete all but the most recent version. The most recent version should
reside in x:\cygwin\bin, where 'x' is the drive on which you have
installed the cygwin distribution. Rebooting is also suggested if you
are unable to find another cygwin DLL.

[jdrews]

It's been happening since January 2022. Here's a build with the same error
https://ci.appveyor.com/project/fstab/grok-exporter/builds/42102402#L415