Bump default dialect to C++14 for clang-cl

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@343437 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/CMakeLists.txt b/CMakeLists.txt
index b560600..7295e01 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -503,7 +503,7 @@
 
 # Required flags ==============================================================
 set(LIBCXX_STANDARD_VER c++11 CACHE INTERNAL "internal option to change build dialect")
-if (LIBCXX_HAS_MUSL_LIBC)
+if (LIBCXX_HAS_MUSL_LIBC OR LIBCXX_TARGETING_CLANG_CL)
   # musl's pthread implementations uses volatile types in their structs which is
   # not a constexpr in C++11 but is in C++14, so we use C++14 with musl.
   set(LIBCXX_STANDARD_VER c++14 CACHE INTERNAL "internal option to change build dialect")