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/implicit-decl.c b/test/Sema/implicit-decl.c
index 099cf9d..91f5dd1 100644
--- a/test/Sema/implicit-decl.c
+++ b/test/Sema/implicit-decl.c
@@ -9,7 +9,7 @@
    int32_t compCount = 0;
    if (_CFCalendarDecomposeAbsoluteTimeV(compDesc, vector, compCount)) { // expected-note {{previous implicit declaration is here}}
    }
-   return ((void *)0);
+   return ((void *)0); // expected-warning {{void function 'func' should not return a value}}
 }
 Boolean _CFCalendarDecomposeAbsoluteTimeV(const char *componentDesc, int32_t **vector, int32_t count) { // expected-error{{conflicting types for '_CFCalendarDecomposeAbsoluteTimeV'}}
  return 0;