libc: Merge header directories for glibc and NetBSD libc where applicable.

Manual patches:

* lib/libc/include/csky-linux-gnu/gnu/{lib-names,stubs}.h
* lib/libc/include/powerpc-linux-gnu/bits/long-double.h

Takes lib/libc/include from 115.5 MB to 113.4 MB.

Closes #21258.
63a9048bafAlex Rønne Petersen committed on 5/29/2025, 10:15:39 PMparent7c7627b
64 files changedLine totals unavailable