CodeGen: mark ObjC cstring literals as unnamed_addr

These are all emitted into a section with a cstring_literal attribute.  The
attribute permits the linker to coalesce the string contents.  The address of
the strings are not important.

llvm-svn: 281855
diff --git a/clang/test/CodeGenObjC/encode-cstyle-method.m b/clang/test/CodeGenObjC/encode-cstyle-method.m
index 0fcbf62..cb1e677 100644
--- a/clang/test/CodeGenObjC/encode-cstyle-method.m
+++ b/clang/test/CodeGenObjC/encode-cstyle-method.m
@@ -8,4 +8,4 @@
 @implementation Foo
 - (id)test:(id )one, id two {return two; } @end
 
-// CHECK-LP64: private constant [11 x i8] c"@24@0:8@16
+// CHECK-LP64: private unnamed_addr constant [11 x i8] c"@24@0:8@16