Fix a mistake in r217762

Summary:
The extra macro definition needs to go into COMPILER_RT_GTEST_CFLAGS
in order to be used for gtests on MSVC2012.

Test Plan: This is part of the fixes necessary for the ASAN tests to pass with MSVC2012.

Reviewers: timurrrr

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D5493

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@218464 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/cmake/Modules/AddCompilerRT.cmake b/cmake/Modules/AddCompilerRT.cmake
index 31bfa22..a3efc8d 100644
--- a/cmake/Modules/AddCompilerRT.cmake
+++ b/cmake/Modules/AddCompilerRT.cmake
@@ -142,7 +142,7 @@
   # Visual Studio 2012 only supports up to 8 template parameters in
   # std::tr1::tuple by default, but gtest requires 10
   if(MSVC_VERSION EQUAL 1700)
-    add_definitions(-D_VARIADIC_MAX=10)
+    list(APPEND COMPILER_RT_GTEST_CFLAGS -D_VARIADIC_MAX=10)
   endif()
 endif()