glsl: build without bison

Removes the hard dependency on bison and makes it possible to build with byacc.

Issues

In order to get this to build, I had to manually patch the files generated from glsl_parser.yy. This is because byacc and bison define YYSTYPE differently.

// byacc generates this
typedef union {...} YYSTYPE;
// bison generates this
union YYSTYPE {...};
typedef union YYSTYPE YYSTYPE;

This breaks the forward declaration of YYSTYPE in glsl_parser_extras.h. I don't know what the best way to fix this would be.

Edit

I was also successful at building Mesa as it is in my fork with the following patch to byacc

--- a/reader.c
+++ b/reader.c
@@ -902,7 +902,7 @@

     if (!lflag)
 	fprintf(text_file, line_format, lineno, input_file_name);
-    puts_both("typedef union");
+    puts_both("typedef union YYSTYPE");

     depth = 0;
   loop: