glsl: process blend_support_* qualifiers

v2 (Ken): Add a BLEND_NONE enum value (no qualifiers in use).
v3 (Ken): Rename gl_blend_support_qualifier to gl_advanced_blend_mode.
v4 (Ken): Mark map[] as static const (Ilia).

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>

src/compiler/glsl/glsl_parser_extras.h

@@ -746,6 +746,8 @@ struct _mesa_glsl_parse_state {
 
    bool fs_early_fragment_tests;
 
+   unsigned fs_blend_support;
+
    /**
     * For tessellation control shaders, size of the most recently seen output
     * declaration that was a sized array, or 0 if no sized output array