glx: Fix glXGetProcAddress() of global glX symbols post-automake conversion.

glx: Fix glXGetProcAddress() of global glX symbols post-automake conversion.

When a GL LD_PRELOAD library like apitrace was used,
glXGetProcAddress() would return the preload's symbols instead of
libGL's symbol, leading to infinite recursion when the returned
function was called.  This didn't hit apitrace on most apps because
who calls glXGetProcAddress() on the global functions.

The -Bsymbolic, which was present in mklib before automake conversion,
causes the glxcmds.c:GLX_functions table to be resolved at link time,
so that LD_PRELOADs don't affect it any more.

Fixes crashes when running wine under apitrace.

Tested-by: Matt Turner <mattst88@gmail.com>
Tested-by: Marek Olšák <maraeo@gmail.com>