Clang: Support Windows variants for GNU and MSVC (#13035, #14458)

Teach the compiler identification preprocessor tests to report when
Clang simulates MSVC, and what version.  If not MSVC, assume GNU.

Teach compiler information modules Clang-(C|CXX) to recognize when Clang
simulates MSVC and skip loading the GNU information.

Teach the Windows-MSVC platform information to recognize when it is
loaded as the simulated compiler and use that version information
instead of the real compiler's (different) version scheme.

Add platform modules Windows-Clang-(C|CXX) and support module
Windows-Clang to load either Windows-MSVC or Windows-GNU and wrap
the corresponding information macros.

4 files changed, 42 insertions, 2 deletions

diff --git a/Modules/Platform/Windows-Clang-C.cmake b/Modules/Platform/Windows-Clang-C.cmake
new file mode 100644
index 0000000..d007105
--- /dev/null
+++ b/Modules/Platform/Windows-Clang-C.cmake
@@ -0,0 +1,2 @@
+include(Platform/Windows-Clang)
+__windows_compiler_clang(C)
diff --git a/Modules/Platform/Windows-Clang-CXX.cmake b/Modules/Platform/Windows-Clang-CXX.cmake
new file mode 100644
index 0000000..2c3688a
--- /dev/null
+++ b/Modules/Platform/Windows-Clang-CXX.cmake
@@ -0,0 +1,2 @@
+include(Platform/Windows-Clang)
+__windows_compiler_clang(CXX)
diff --git a/Modules/Platform/Windows-Clang.cmake b/Modules/Platform/Windows-Clang.cmake
new file mode 100644
index 0000000..4c936fe
--- /dev/null
+++ b/Modules/Platform/Windows-Clang.cmake
@@ -0,0 +1,32 @@
+
+#=============================================================================
+# Copyright 2001-2013 Kitware, Inc.
+#
+# Distributed under the OSI-approved BSD License (the "License");
+# see accompanying file Copyright.txt for details.
+#
+# This software is distributed WITHOUT ANY WARRANTY; without even the
+# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+# See the License for more information.
+#=============================================================================
+# (To distribute this file outside of CMake, substitute the full
+#  License text for the above reference.)
+
+# This module is shared by multiple languages; use include blocker.
+if(__WINDOWS_CLANG)
+  return()
+endif()
+set(__WINDOWS_CLANG 1)
+
+if(CMAKE_C_SIMULATE_ID STREQUAL "MSVC"
+    OR CMAKE_CXX_SIMULATE_ID STREQUAL "MSVC")
+  include(Platform/Windows-MSVC)
+  macro(__windows_compiler_clang lang)
+    __windows_compiler_msvc(${lang})
+  endmacro()
+else()
+  include(Platform/Windows-GNU)
+  macro(__windows_compiler_clang lang)
+    __windows_compiler_gnu(${lang})
+  endmacro()
+endif()
diff --git a/Modules/Platform/Windows-MSVC.cmake b/Modules/Platform/Windows-MSVC.cmake
index 7036ba0..a2cfe33 100644
--- a/Modules/Platform/Windows-MSVC.cmake
+++ b/Modules/Platform/Windows-MSVC.cmake
@@ -65,7 +65,11 @@ else()
 endif()
 
 if(NOT MSVC_VERSION)
-  if(CMAKE_C_COMPILER_VERSION)
+  if(CMAKE_C_SIMULATE_VERSION)
+    set(_compiler_version ${CMAKE_C_SIMULATE_VERSION})
+  elseif(CMAKE_CXX_SIMULATE_VERSION)
+    set(_compiler_version ${CMAKE_CXX_SIMULATE_VERSION})
+  elseif(CMAKE_C_COMPILER_VERSION)
     set(_compiler_version ${CMAKE_C_COMPILER_VERSION})
   else()
     set(_compiler_version ${CMAKE_CXX_COMPILER_VERSION})
@@ -220,7 +224,7 @@ set (CMAKE_MODULE_LINKER_FLAGS_RELEASE_INIT ${CMAKE_EXE_LINKER_FLAGS_RELEASE_INI
 set (CMAKE_MODULE_LINKER_FLAGS_MINSIZEREL_INIT ${CMAKE_EXE_LINKER_FLAGS_MINSIZEREL_INIT})
 
 macro(__windows_compiler_msvc lang)
-  if(NOT "${CMAKE_${lang}_COMPILER_VERSION}" VERSION_LESS 14)
+  if(NOT MSVC_VERSION LESS 1400)
     # for 2005 make sure the manifest is put in the dll with mt
     set(_CMAKE_VS_LINK_DLL "<CMAKE_COMMAND> -E vs_link_dll ")
     set(_CMAKE_VS_LINK_EXE "<CMAKE_COMMAND> -E vs_link_exe ")