libuuid: fix uuid_time on macOS without attribute((alias))

libuuid: fix uuid_time on macOS without attribute((alias))

Weak aliases are not supported by clang on Darwin.
Instead this fix uses inline asm to make `_uuid_time` an alias to
`___uuid_time`

It appears that on macOS the time API is purely 32 or 64 bit depending
on the build type. There is no ABI issue on that platform and `uuid_time`
can be unconditionally aliased to `_uuid_time`. This is all conjectural,
however, since I have no ability to make 32-bit builds for macOS - the
Apple toolchain doesn't support this since 2019.

Fixes util-linux/util-linux#2873