allow leading "L" prefix for string constants

src/parser/parser.l

@@ -121,7 +121,7 @@ L?'\\v'             (void)'\v'; return TOK_CHAR_CONST;
 0[xX][0-9a-fA-F]+([uU][lL]?[lL]?)?   return TOK_INT_CONST;
 ([0-9]+\.[0-9]*|\.[0-9]+)([eE][-+]?[0-9]+)?[fFlL]?     return TOK_FLOAT_CONST;
 
-\" {
+L?\" {
     if (build_string != NULL)
     {
         String_free(build_string);