cmake: Don't do the libstdc++ version check when clang simulates MSVC

If we're using clang-cl, that's a pretty good indication that we're
going to use MSVC's STL.

This simplifies the clang-cl ninja self-host configuration down to:
CC=clang-cl CXX=clang-cl cmake .. -GNinja

Modified version of zturner's patch:
Differential Revision: http://reviews.llvm.org/D7824

llvm-svn: 230239

1 files changed, 9 insertions, 5 deletions

diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
index ba6114a4f56..14fda9284c9 100644
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -21,11 +21,15 @@ if(NOT LLVM_FORCE_USE_OLD_TOOLCHAIN)
       message(FATAL_ERROR "Host Clang version must be at least 3.1!")
     endif()
 
-    # Also test that we aren't using too old of a version of libstdc++ with the
-    # Clang compiler. This is tricky as there is no real way to check the
-    # version of libstdc++ directly. Instead we test for a known bug in
-    # libstdc++4.6 that is fixed in libstdc++4.7.
-    if(NOT LLVM_ENABLE_LIBCXX)
+    if (CMAKE_CXX_SIMULATE_ID MATCHES "MSVC")
+      if (CMAKE_CXX_SIMULATE_VERSION VERSION_LESS 18.0)
+        message(FATAL_ERROR "Host Clang must have at least -fms-compatibility-version=18.0")
+      endif()
+    elseif(NOT LLVM_ENABLE_LIBCXX)
+      # Otherwise, test that we aren't using too old of a version of libstdc++
+      # with the Clang compiler. This is tricky as there is no real way to
+      # check the version of libstdc++ directly. Instead we test for a known
+      # bug in libstdc++4.6 that is fixed in libstdc++4.7.
       set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
       set(OLD_CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES})
       set(CMAKE_REQUIRED_FLAGS "-std=c++0x")