c11: Improve timespec_get to support TIME_MONOTONIC TIME_ACTIVE TIME_THREAD_ACTIVE TIME_MONOTONIC_RAW

As c11 already provided timespec_get, to avoid symbol conflict, use c23_timespec_get as the function name
and define timespec_get c23_timespec_get to achieve that

Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Acked-by: David Heidelberg <david.heidelberg@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23733>

meson.build

@@ -1282,7 +1282,6 @@ endforeach
 functions_to_detect = {
   'strtof': '',
   'mkostemp': '',
-  'timespec_get': '#include <time.h>',
   'memfd_create': '',
   'random_r': '',
   'flock': '',