glsl: Classify "layout" like other identifiers.

When "layout" isn't being lexed as LAYOUT_TOK, we should treat it like
an ordinary identifier.  This means we need to classify it to determine
whether we should return IDENTIFIER, TYPE_IDENTIFIER, or NEW_IDENTIFIER.

Fixes the WebGL conformance test "shader-with-non-reserved-words."

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=64087
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Cc: mesa-stable@lists.freedesktop.org

src/glsl/glsl_lexer.ll

@@ -352,7 +352,7 @@ layout		{
 		      return LAYOUT_TOK;
 		   } else {
 		      yylval->identifier = strdup(yytext);
-		      return IDENTIFIER;
+		      return classify_identifier(yyextra, yytext);
 		   }
 		}