c-decl.c (finish_function): Warn about a non-void function with no return…

c-decl.c (finish_function): Warn about a non-void function with no return statement and no abnormal exit.

        * c-decl.c (finish_function): Warn about a non-void function with
        no return statement and no abnormal exit.
        (current_function_returns_abnormally): New variable.
        (start_function): Clear it.
        (struct c_language_function): Add returns_abnormally.
        (push_c_function_context): Save it.
        (pop_c_function_context): Restore it.
        (builtin_function): Set TREE_THIS_VOLATILE on return fns.
        (grokdeclarator): Set C_FUNCTION_IMPLICIT_INT on functions without
        an explicit return type.
        * c-tree.h: Declare current_function_returns_abnormally.
        (C_FUNCTION_IMPLICIT_INT): New macro.
        * c-typeck.c (build_function_call): Set it.
        (c_expand_return): Set current_function_returns_value even if the
        value is erroneous.

From-SVN: r49579

gcc/testsuite/gcc.dg/Wreturn-type2.c

+/* Test for cases that should not get the unconditional warning about
+   missing return.  */
+/* { dg-do compile } */
+
+f() {}				/* { dg-bogus "" "no return warning" } */
+int g() { abort (); }		/* { dg-bogus "" "no return warning" } */
+int main() {}			/* { dg-bogus "" "no return warning" } */