Require Visual Studio 2013 or later.

Change-Id: I440bdc7126a5ea0762418181fc5b6a86df92d1aa
Reviewed-on: https://code-review.googlesource.com/4267
Reviewed-by: Paul Wankadia <junyer@google.com>

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0212a0b..3ed718f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -11,14 +11,18 @@
 
 set(EXTRA_TARGET_LINK_LIBRARIES)
 
-if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
+if(CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
+  if(MSVC_VERSION LESS 1800)
+    message(FATAL_ERROR "you need Visual Studio 2013 or later")
+  endif()
+elseif(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
   add_compile_options(-std=c++11)
 endif()
 
 if(WIN32)
   add_definitions(-DUNICODE -D_UNICODE -DSTRICT -DNOMINMAX)
   set(THREADING threadwin)
-else()
+elseif(UNIX)
   add_compile_options(-pthread)
   set(THREADING thread)
   list(APPEND EXTRA_TARGET_LINK_LIBRARIES -pthread)