windows: move INLINE macro, remove UNUSED

Move the INLINE macro from src/uv-common.h to src/win/internal.h, it's
not used in src/unix/ or src/

Remove the UNUSED macro. It's, well, unused.
unix: clean up __attribute__((quux)) usage

Macro-ify __attribute__((destructor)) and __attribute__((unused)).

The macros are no-ops when the compiler does not support function
attributes.
sunos: remove futimes() macro

Remove a macro from src/unix/internal.h that aliases futimes() to
futimesat(). Deal with the platform inconsistency in src/unix/fs.c.
unix: fix uv__signal_unlock() prototype