glsl: Generate ir_expression_operation.h from Python

There are differences in where end-of-line comments are placed, but
'diff -wud' is clean.

v2: Massive rebase.

v3: With much help from José Fonseca, fix SCons build.

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

src/mesa/SConscript

@@ -11,6 +11,7 @@ env.MSVC2013Compat()
 
 env.Append(CPPPATH = [
     '../compiler/nir',  # for generated nir_opcodes.h, etc
+    '../compiler/glsl',  # for generated headers
     '#/src',
     Dir('../mapi'), # src/mapi build path
     '#/src/mapi',