glsl: Add pragma to disable all warnings

glsl: Add pragma to disable all warnings

Use #pragma warning(off) and #pragma warning(on) to disable or enable
all warnings.  This is a big hammer.  If we ever need a smaller hammer,
we can enhance this functionality.

There is one lame thing about this.  Because we parse everything, create
an AST, then convert the AST to GLSL IR, we have to treat the #pragma
like a statment.  This means that you can't do something like

'    void
'    #pragma warning(off)
'    __foo
'    #pragma warning(on)
'    (float param0);

Fixing that would, as far as I can tell, require a huge amount of work.

I did try just handling the #pragma during parsing (like we do for
state for the whole shader.

v2: Fix the #pragma lines in the commit message that git-commit ate.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>