glut: Do not rely on GLAPIENTRY symbol.

glut: Do not rely on GLAPIENTRY symbol.

GLEW does some defining/undefining of GLAPIENTRY making it unreliable. GLEW
should also be fixed, but removing the dependency on this symbol.

This also restores the ability for GLUT to be used with -fvisibility=hidden.
The downside of this is that ld warns of:

  Warning: size of symbol `glutBitmapXXXXX' changed from 4 in glut_xxx.o to 16 in glut_xxxx.o

Due to the fonts being declared void * (*4 bytes), but defined as 16byte static
structure. I'll fix that in a later commit.

See also commits:
 - f321f16e83cae427d6496c11955fd1c898d0395c
 - d084982240bafba0169c4a6cacf02d45d6cfd8c1