[libc++] Split a few utilities out of __threading_support

This change is the basis for a further refactoring where I'm going to
split up the various implementations we have in __threading_support to
make that code easier to understand.

Note that I had to make __convert_to_timespec a template to break
circular dependencies. Concretely, we never seem to use it with anything
other than ::timespec, but I am wary of hardcoding that assumption as
part of this change, since I suspect there's a reason for going through
these hoops in the first place.

Differential Revision: https://reviews.llvm.org/D116944

0 files changed, 0 insertions, 0 deletions