Enable larger tuple sizes for Visual Studio 2012.

Visual Studio 2012 does not have variadic templates and implements
tuples differently. By default, only sizes up to 5 are supported,
which conflicts with Gtest.

Change-Id: Ieb8d59e4329863cbfa2729d8a76db0714c08d259

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 43d4430..a7b77fe 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -634,6 +634,9 @@
   # which results in linker warnings. This is irrelevant for Ceres, so ignore
   # the warnings.
   SET(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} /ignore:4049")
+
+  # Tuple sizes of 10 are used by Gtest.
+  ADD_DEFINITIONS("-D_VARIADIC_MAX=10")
 ENDIF (MSVC)
 
 # GCC is not strict enough by default, so enable most of the warnings.