They compile fine for me with ABI_X86="64 32" Reproducible: Always
I don't think they're multilib because they don't need to be. All of the installed files are platform independent. I'm CC'ing mgorny so he can confirm and close the bug.
What does need them for multilib? We aren't ready for gl libs yet. @Pacho, xorg proto packages install pkg-config files in libdir. We multilib them in case headers started to differ per-ABI.
libdir is not checked by 32-bit stuff.
Bump
I will close this as dup of opengl multilib bug since we will be doing all the multilib stuff in one go. *** This bug has been marked as a duplicate of bug 468102 ***