Regression test for current cpplib bug.

Should not fail if you are using cccp.
Expect it to fail if you are using cpplib.

From-SVN: r26224

gcc/testsuite/gcc.dg/990407-1.c

+/* Regression test for a cpplib macro-expansion bug where
+   `@' becomes `@@' when stringified.  */
+
+/* { dg-do run } */
+
+#include <string.h>
+
+#define STR(x) #x
+
+char *a = STR(@foo), *b = "@foo";
+
+int
+main(void)
+{
+  if (strcmp (a, b))
+    abort ();
+  return 0;
+}