New tests for noreturn.

From-SVN: r38611

gcc/testsuite/gcc.dg/noreturn-3.c

+/* Check for no "noreturn" warning in main. */
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wmissing-noreturn -fhosted" } */
+extern void exit (int) __attribute__ ((__noreturn__));
+
+int
+main (void)
+{
+  exit (0);
+}

gcc/testsuite/gcc.dg/noreturn-4.c

+/* Check for "noreturn" warning in main. */
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wmissing-noreturn -ffreestanding" } */
+extern void exit (int) __attribute__ ((__noreturn__));
+
+int
+main (void)
+{
+  exit (0);
+} /* { dg-warning "warning: function might be possible candidate for attribute `noreturn'" "warn for main" } */