[Mesa-dev] v2 GLSL compile time improvements

[Timothy Arceri]

v2: Address various comments from Thomas. All minor but enough
 to warrant a resend.

I've sent all but the last 2 already but they haven't received much
feedback yet.

This series reduces compile times of the Deus Ex shaders on my
Ryzen 1800X from 2m27s -> 2m8s with a cold cache on radeonsi.

Note: The above times are from compiling the shaders with shader-db
on a single thread, starting the actual game results in around
double the time/improvement.

The aim of the series was to target overhead in the parser/AST
sections of the compiler. I believe there is probably still more
low hanging fruit in the AST code. I've been profiling this by
compiling the shaders once and then deleting the index file from
the cache.

Please review.