12 files changed, 45 insertions, 12 deletions
diff --git a/Tests/AliasTarget/CMakeLists.txt b/Tests/AliasTarget/CMakeLists.txt
index fc70135..6271988 100644
--- a/Tests/AliasTarget/CMakeLists.txt
+++ b/Tests/AliasTarget/CMakeLists.txt
@@ -7,7 +7,7 @@ set(CMAKE_CXX_STANDARD 98)
 # 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)
+  set(CMAKE_CXX_STANDARD 14)
 endif()
 
 add_library(foo SHARED empty.cpp)
diff --git a/Tests/COnly/CMakeLists.txt b/Tests/COnly/CMakeLists.txt
index b3cc438..3037f13 100644
--- a/Tests/COnly/CMakeLists.txt
+++ b/Tests/COnly/CMakeLists.txt
@@ -7,7 +7,7 @@ add_library(testc1 STATIC libc1.c)
 add_library(testc2 SHARED libc2.c)
 add_executable (COnly conly.c foo.c foo.h)
 target_link_libraries(COnly testc1 testc2)
-if(MSVC_VERSION)
+if(MSVC_VERSION AND NOT CMAKE_C_COMPILER_ID STREQUAL Clang OR "x${CMAKE_C_COMPILER_FRONTEND_VARIANT}" STREQUAL "xMSVC")
   set_target_properties(COnly PROPERTIES
     LINK_FLAGS " /NODEFAULTLIB:\"libcdg.lib\" /NODEFAULTLIB:\"libcmtg.lib\" /NODEFAULTLIB:\"foomsvcrt.lib\" /NODEFAULTLIB:\"libbar.lib\" /NODEFAULTLIB:\"libfooba.lib\"")
 endif()
diff --git a/Tests/Complex/CMakeLists.txt b/Tests/Complex/CMakeLists.txt
index 2e41754..fef83f6 100644
--- a/Tests/Complex/CMakeLists.txt
+++ b/Tests/Complex/CMakeLists.txt
@@ -446,6 +446,11 @@ if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND
   set(CMAKE_CXX_STANDARD 11)
 endif()
 
+if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND
+    CMAKE_CXX_COMPILER_FRONTEND_VARIANT STREQUAL "GNU")
+  set(CMAKE_CXX_STANDARD 14)
+endif()
+
 #
 # Create the libs and the main exe
 #
diff --git a/Tests/ComplexOneConfig/CMakeLists.txt b/Tests/ComplexOneConfig/CMakeLists.txt
index 628cd4e..77baa4c 100644
--- a/Tests/ComplexOneConfig/CMakeLists.txt
+++ b/Tests/ComplexOneConfig/CMakeLists.txt
@@ -403,6 +403,11 @@ if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND
   set(CMAKE_CXX_STANDARD 11)
 endif()
 
+if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND
+    CMAKE_CXX_COMPILER_FRONTEND_VARIANT STREQUAL "GNU")
+  set(CMAKE_CXX_STANDARD 14)
+endif()
+
 #
 # Create the libs and the main exe
 #
diff --git a/Tests/EnforceConfig.cmake.in b/Tests/EnforceConfig.cmake.in
index 8c0817c..b8a6860 100644
--- a/Tests/EnforceConfig.cmake.in
+++ b/Tests/EnforceConfig.cmake.in
@@ -18,7 +18,12 @@ if(NOT CTEST_CONFIGURATION_TYPE)
     endif()
   endforeach()
   if(NOT CTEST_CONFIGURATION_TYPE)
-    set(CTEST_CONFIGURATION_TYPE NoConfig)
+    if("@CMAKE_C_COMPILER_ID@;@CMAKE_C_SIMULATE_ID@;@CMAKE_C_COMPILER_FRONTEND_VARIANT@" STREQUAL "Clang;MSVC;GNU")
+      # A valid configuration is required for this compiler in tests that do not set CMP0091 to NEW.
+      set(CTEST_CONFIGURATION_TYPE Debug)
+    else()
+      set(CTEST_CONFIGURATION_TYPE NoConfig)
+    endif()
   endif()
   message("Guessing configuration ${CTEST_CONFIGURATION_TYPE}")
 endif()
diff --git a/Tests/Module/WriteCompilerDetectionHeader/CMakeLists.txt b/Tests/Module/WriteCompilerDetectionHeader/CMakeLists.txt
index cffef5a..b30928d 100644
--- a/Tests/Module/WriteCompilerDetectionHeader/CMakeLists.txt
+++ b/Tests/Module/WriteCompilerDetectionHeader/CMakeLists.txt
@@ -133,7 +133,9 @@ endif()
 
 # for msvc the compiler version determines which c++11 features are available.
 if (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC"
-    OR (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND "x${CMAKE_CXX_SIMULATE_ID}" STREQUAL "xMSVC"))
+    OR (CMAKE_CXX_COMPILER_ID STREQUAL "Clang"
+    AND "x${CMAKE_CXX_SIMULATE_ID}" STREQUAL "xMSVC"
+    AND "x${CMAKE_CXX_COMPILER_FRONTEND_VARIANT}" STREQUAL "xMSVC" ))
   if(";${CMAKE_CXX_COMPILE_FEATURES};" MATCHES ";cxx_delegating_constructors;")
     list(APPEND true_defs EXPECTED_COMPILER_CXX_DELEGATING_CONSTRUCTORS)
     list(APPEND true_defs EXPECTED_COMPILER_CXX_VARIADIC_TEMPLATES)
diff --git a/Tests/Plugin/CMakeLists.txt b/Tests/Plugin/CMakeLists.txt
index 8e8fa07..c4540db 100644
--- a/Tests/Plugin/CMakeLists.txt
+++ b/Tests/Plugin/CMakeLists.txt
@@ -5,6 +5,17 @@ project(Plugin)
 # We need proper C++98 support from the compiler
 set(CMAKE_CXX_STANDARD 98)
 
+# 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()
+
+if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND
+    CMAKE_CXX_COMPILER_FRONTEND_VARIANT STREQUAL "GNU")
+  set(CMAKE_CXX_STANDARD 14)
+endif()
+
 # Test per-target output directory properties.
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${Plugin_BINARY_DIR}/bin)
 set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${Plugin_BINARY_DIR}/lib/plugin)
@@ -29,12 +40,6 @@ include_directories(
   ${Plugin_SOURCE_DIR}/include
   )
 
-# 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
diff --git a/Tests/RunCMake/GenerateExportHeader/GEH.cmake b/Tests/RunCMake/GenerateExportHeader/GEH.cmake
index ae9a84c..b3f1c7f 100644
--- a/Tests/RunCMake/GenerateExportHeader/GEH.cmake
+++ b/Tests/RunCMake/GenerateExportHeader/GEH.cmake
@@ -51,6 +51,11 @@ if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND
   set(CMAKE_CXX_STANDARD 11)
 endif()
 
+if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND
+    CMAKE_CXX_COMPILER_FRONTEND_VARIANT STREQUAL "GNU")
+  set(CMAKE_CXX_STANDARD 14)
+endif()
+
 add_subdirectory(lib_shared_and_static)
 
 if(CMAKE_SYSTEM_NAME MATCHES "AIX" AND CMAKE_CXX_COMPILER_ID STREQUAL "GNU"
diff --git a/Tests/RunCMake/Ninja/greeting.c b/Tests/RunCMake/Ninja/greeting.c
index ba3e55b..1124d14 100644
--- a/Tests/RunCMake/Ninja/greeting.c
+++ b/Tests/RunCMake/Ninja/greeting.c
@@ -6,4 +6,5 @@ __declspec(dllexport)
   void greeting(void)
 {
   printf("Hello world!\n");
+  fflush(stdout);
 }
diff --git a/Tests/RunCMake/Ninja/greeting2.c b/Tests/RunCMake/Ninja/greeting2.c
index c6ed87d..cc8409c 100644
--- a/Tests/RunCMake/Ninja/greeting2.c
+++ b/Tests/RunCMake/Ninja/greeting2.c
@@ -3,4 +3,5 @@
 void greeting2(void)
 {
   printf("Hello world 2!\n");
+  fflush(stdout);
 }
diff --git a/Tests/RunCMake/try_compile/LinkOptions.cmake b/Tests/RunCMake/try_compile/LinkOptions.cmake
index 488cab1..7fae35c 100644
--- a/Tests/RunCMake/try_compile/LinkOptions.cmake
+++ b/Tests/RunCMake/try_compile/LinkOptions.cmake
@@ -5,7 +5,9 @@ cmake_policy(SET CMP0054 NEW)
 
 set (lib_name "${CMAKE_CURRENT_BINARY_DIR}/${CMAKE_STATIC_LIBRARY_PREFIX}lib${CMAKE_STATIC_LIBRARY_SUFFIX}")
 if (CMAKE_SYSTEM_NAME STREQUAL "Windows")
-  if (RunCMake_C_COMPILER_ID STREQUAL "MSVC" OR "x${CMAKE_C_SIMULATE_ID}" STREQUAL "xMSVC")
+  if (RunCMake_C_COMPILER_ID STREQUAL "MSVC"
+      OR ("x${CMAKE_C_SIMULATE_ID}" STREQUAL "xMSVC" AND
+          NOT CMAKE_C_COMPILER_ID STREQUAL "Clang" OR "x${CMAKE_C_COMPILER_FRONTEND_VARIANT}" STREQUAL "xMSVC"))
     if (CMAKE_SIZEOF_VOID_P EQUAL 4)
       set (undef_flag /INCLUDE:_func)
     else()
diff --git a/Tests/RunCMake/try_run/LinkOptions.cmake b/Tests/RunCMake/try_run/LinkOptions.cmake
index 9939a42..b9a87f3 100644
--- a/Tests/RunCMake/try_run/LinkOptions.cmake
+++ b/Tests/RunCMake/try_run/LinkOptions.cmake
@@ -5,7 +5,9 @@ cmake_policy(SET CMP0054 NEW)
 
 set (lib_name "${CMAKE_CURRENT_BINARY_DIR}/${CMAKE_STATIC_LIBRARY_PREFIX}lib${CMAKE_STATIC_LIBRARY_SUFFIX}")
 if (CMAKE_SYSTEM_NAME STREQUAL "Windows")
-  if (RunCMake_C_COMPILER_ID STREQUAL "MSVC" OR "x${CMAKE_C_SIMULATE_ID}" STREQUAL "xMSVC")
+  if (RunCMake_C_COMPILER_ID STREQUAL "MSVC"
+      OR ("x${CMAKE_C_SIMULATE_ID}" STREQUAL "xMSVC" AND
+          NOT CMAKE_C_COMPILER_ID STREQUAL "Clang" OR "x${CMAKE_C_COMPILER_FRONTEND_VARIANT}" STREQUAL "xMSVC"))
     if (CMAKE_SIZEOF_VOID_P EQUAL 4)
       set (undef_flag /INCLUDE:_func)
     else()