Fix MSVC version check to support use of clang-cl front-end

- Raised as issue: #521

Change-Id: Iaea6b43484b90ec8789bda0447c8a90759974ec1

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 76e08d0..2a6b376 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -57,7 +57,8 @@
 mark_as_advanced(CMAKE_CXX_STANDARD_REQUIRED)
 
 # MSVC versions < 2013 did not fully support >= C++11.
-if (MSVC AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 12.0)
+if (CMAKE_CXX_COMPILER_ID MATCHES MSVC AND
+    CMAKE_CXX_COMPILER_VERSION VERSION_LESS 12.0)
   message(FATAL_ERROR "Invalid CMAKE_CXX_COMPILER_VERSION: "
     "${CMAKE_CXX_COMPILER_VERSION}. Ceres requires at least MSVC 2013 Update 4+")
 endif()