Tests: fix Plugin building on Clang/C2

Tests/Plugin/CMakeLists.txt

 cmake_minimum_required (VERSION 2.6)
+cmake_policy(SET CMP0054 NEW)
 project(Plugin)
 
 # Test per-target output directory properties.
@@ -34,6 +35,12 @@ if (CMAKE_CXX_COMPILER_ID STREQUAL HP AND
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -AA")
 endif ()
 
+# Clang/C2 in C++98 mode cannot properly handle some of MSVC headers
+if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND
+    CMAKE_CXX_SIMULATE_ID STREQUAL "MSVC")
+  set(CMAKE_CXX_STANDARD 11)
+endif()
+
 # Create an executable that exports an API for use by plugins.
 add_executable(example_exe src/example_exe.cxx)
 set_target_properties(example_exe PROPERTIES