arm: Fix an rtl checking failure in cde-errors.c

cde-errors.c and cde-mve-error-2.c were failing with an rtl checking
failure because we applied UINTVAL to a nonconstant argument
(specifically a REG).

2020-04-27  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* config/arm/arm-builtins.c (arm_expand_builtin_args): Only apply
	UINTVAL to CONST_INTs.

gcc/ChangeLog

+2020-04-27  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* config/arm/arm-builtins.c (arm_expand_builtin_args): Only apply
+	UINTVAL to CONST_INTs.
+
 2020-04-27  Srinath Parvathaneni  <srinath.parvathaneni@arm.com>
 
 	* config/arm/constraints.md (e): Remove constraint.

gcc/config/arm/arm-builtins.c

@@ -3081,7 +3081,8 @@ constant_arg:
 		    {
 		      if (argc == 0)
 			{
-			  unsigned int cp_bit = UINTVAL (op[argc]);
+			  unsigned int cp_bit = (CONST_INT_P (op[argc])
+						 ? UINTVAL (op[argc]) : -1);
 			  if (IN_RANGE (cp_bit, 0, ARM_CDE_CONST_COPROC))
 			    error ("%Kcoprocessor %d is not enabled "
 				   "with +cdecp%d", exp, cp_bit, cp_bit);