There were some frustrating problems with the implementation of
-Wwrite-strings. First and foremost, once the positive form of the flag
was passed, it could never be disabled by passing -Wno-write-strings.
Also, the diagnostic engine couldn't in turn use -Wwrite-strings to
control diagnostics (as GCC does) because it was essentially hijacked to
drive the language semantics.

Fix this by giving CC1 a clean '-fconst-strings' flag to enable
const-qualified strings in C and ObjC compilations. Corresponding
'-fno-const-strings' is also added. Then the driver is taught to
introduce '-fconst-strings' in the CC1 command when '-Wwrite-strings'
dominates.

This entire flag is basically GCC-bug-compatibility driven, so we also
match GCC's bug where '-w' doesn't actually disable -Wwrite-strings. I'm
open to changing this though as it seems insane.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@130051 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Sema/warn-write-strings.c b/test/Sema/warn-write-strings.c
index dd0bb8a..dee554c 100644
--- a/test/Sema/warn-write-strings.c
+++ b/test/Sema/warn-write-strings.c
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -verify -fsyntax-only -Wwrite-strings %s
+// RUN: %clang_cc1 -verify -fsyntax-only -fconst-strings %s
 
 // PR4804
 char* x = "foo"; // expected-warning {{initializing 'char *' with an expression of type 'const char [4]' discards qualifiers}}