Specify -std=gnu++98 on some Rewriter tests. NFC.

Rewriter tests rewrite Objective-C++ to C++, and then compile the
result.  The rewritten result sometimes doesn't work with C++11.  As
we want to allow Clang's default dialect to become C++11, we need to
make sure the tests will still pass.

llvm-svn: 289167
diff --git a/clang/test/Rewriter/rewrite-modern-class.mm b/clang/test/Rewriter/rewrite-modern-class.mm
index b6be98a..cf2143e 100644
--- a/clang/test/Rewriter/rewrite-modern-class.mm
+++ b/clang/test/Rewriter/rewrite-modern-class.mm
@@ -1,5 +1,5 @@
 // RUN: %clang_cc1 -x objective-c++ -Wno-return-type -fblocks -fms-extensions -rewrite-objc %s -o %t-rw.cpp
-// RUN: %clang_cc1 -fsyntax-only -fblocks -Wno-address-of-temporary -D"Class=void*" -D"id=void*" -D"SEL=void*" -D"__declspec(X)=" %t-rw.cpp
+// RUN: %clang_cc1 -fsyntax-only -std=gnu++98 -fblocks -Wno-address-of-temporary -D"Class=void*" -D"id=void*" -D"SEL=void*" -D"__declspec(X)=" %t-rw.cpp
 
 @protocol PROTO @end