android: Fix ELF TLS support.

android: Fix ELF TLS support.

Android 29 introduced general-dynamic TLS variable support ("quick
function call to look up the location of the dynamically allocated
storage"), while Mesa on normal Linux has used initial-exec ("use some of
the startup-time fixed slots, hope for the best!").  Both would be better
options than falling all the way back to pthread_getspecific(), which is
the alternative we have pre-29.

Reviewed-by: Roman Stratiienko <r.stratiienko@gmail.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10389>