Fix redefinition of `clock_gettime` and `clock_getres`
winpthreads-git 12.0.0.r720 provides `clock_gettime` and
`clock_getres` as inline functions.
digest.so needs ruby/digest.h which is installed by build-ext
Copy to path with the base name
Related issues
Bug #21327: Windows builds seem broken after clock_gettime changes?
merge revision(s) 3e47e7a499acd256be549935fcb559d3c82e556c, b48b841378f80e16378ceb83f3b78e52df9ae023, 2fe8b9cd3d308d754f3d33a948dfb1dd782a10dc: [Backport #21327]