glx: Use GLX_FUNCTION2 only for actually aliased function names

glx: Use GLX_FUNCTION2 only for actually aliased function names

I find the __glX naming convention distasteful for a bunch of reasons,
not least that I expect "vi -t glXBindTexImageEXT" to take me someplace
useful. The functions we're referencing here should not be exported from
libGL (hence the static / _X_HIDDEN) but that's no reason not to name
them correctly.

This does have one possible, very minor, correct functional change,
glXGetMscRateOML now returns Bool (unsigned int) instead of GLboolean
(unsigned char); if your psABI really only writes to a single byte of
the return register when the return type is char-like, then we probably
would not have returned false when we meant to. At least for amd64 this
does not seem to be an issue; the old code wrote 0 to %eax, the new code
does a zero-extended load from %al to %eax (since the internal function
still returns GLboolean).

Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6671>