glsl: Don't inline function prototypes.

glsl: Don't inline function prototypes.

Currently, the standalone compiler tries to do function inlining before
linking shaders (including linking against the built-in functions).
This resulted in the built-in function _prototypes_ being inlined rather
than the actual function definition.

This is only known to fix a bug in the standalone compiler; most
programs should be unaffected.  Still, it seems like a good idea.

NOTE: This is a candidate for the 7.9 branch.