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/compiler/SConscript

@@ -13,6 +13,10 @@ env.Prepend(CPPPATH = [
     '#src/gallium/auxiliary',
 ])
 
+# Make generated headers reachable from the include path.
+env.Prepend(CPPPATH = [Dir('.').abspath, Dir('glsl').abspath])
+env.Prepend(CPPPATH = [Dir('.').abspath, Dir('nir').abspath])
+
 sources = env.ParseSourceList('Makefile.sources', 'LIBCOMPILER_FILES')
 
 compiler = env.ConvenienceLibrary(