Added to test Objective-C strings.

From-SVN: r35333

gcc/testsuite/objc/execute/string1.m

+#include <stdio.h>
+#include <objc/NXConstStr.h>
+
+int main(int argc, void **args)
+{
+  printf ([@"this is a string\n" cString]);
+  return 0;
+}

gcc/testsuite/objc/execute/string2.m

+#include <stdio.h>
+#include <objc/NXConstStr.h>
+
+int main(int argc, void **args)
+{
+  printf ([@"this " @"is " @"a " @"string\n" cString]);
+  return 0;
+}