testsuite: mark tests that require alias

gcc/testsuite/ChangeLog:

	* gcc.dg/pr100509.c: Needs alias.
	* gcc.dg/pragma-diag-10.c: Needs alias.

gcc/testsuite/gcc.dg/pr100509.c

@@ -1,5 +1,6 @@
 /* { dg-do compile } */
 /* { dg-options "-O" } */
+/* { dg-require-alias "" } */
 
 struct X {
   int a;

gcc/testsuite/gcc.dg/pragma-diag-10.c

@@ -1,7 +1,8 @@
 /* PR middle-end/98512 - #pragma GCC diagnostic ignored ineffective
    in conjunction with alias attribute
    { dg-do compile }
-   { dg-options "-O2 -Wall" } */
+   { dg-options "-O2 -Wall" }
+   { dg-require-alias "" } */
 
 void *
 __rawmemchr_ppc (const void *s, int c)