Merge function-return.c into function.c

Fix PR2790 by making a warning an EXTWARN instead of EXTENSION.
Add a new EXTENSION warning for "return (some void expression);"


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@61187 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Sema/function.c b/test/Sema/function.c
index f2aa8d9..de970a0 100644
--- a/test/Sema/function.c
+++ b/test/Sema/function.c
@@ -32,3 +32,10 @@
 // PR3208
 void t12(int) {}  // expected-error{{parameter name omitted}}
 
+// PR2790
+void t13() {
+  return 0; // expected-warning {{void function 't13' should not return a value}}
+}
+int t14() {
+  return; // expected-warning {{non-void function 't14' should return a value}}
+}