Tests: Fix RunCMake.try_compile CxxStandard case on MSVC

In post-3.9 development we've taught CMake to understand C++ language
standards for MSVC.  The RunCMake.try_compile test needs to know whether
to expect support or not.  Previously we depended on the host CMake
version to know this, but CMake 3.9 and below do not.  Add special logic
to the test to account for this.

Tests/RunCMake/CMakeLists.txt

@@ -227,20 +227,38 @@ add_RunCMake_test(separate_arguments)
 add_RunCMake_test(set_property)
 add_RunCMake_test(string)
 add_RunCMake_test(test_include_dirs)
-foreach(var
-    CMAKE_C_COMPILER_ID
-    CMAKE_C_COMPILER_VERSION
-    CMAKE_C_STANDARD_DEFAULT
-    CMAKE_CXX_COMPILER_ID
-    CMAKE_CXX_COMPILER_VERSION
-    CMAKE_CXX_STANDARD_DEFAULT
-    CMake_TEST_CUDA
-    )
-  if(DEFINED ${var})
-    list(APPEND try_compile_ARGS -D${var}=${${var}})
+
+function(add_RunCMake_test_try_compile)
+  if(CMAKE_VERSION VERSION_LESS 3.9.20170907 AND "x${CMAKE_CXX_COMPILER_ID}" STREQUAL "xMSVC")
+    # Older CMake versions do not know about MSVC language standards.
+    # Approximate our logic from MSVC-CXX.cmake.
+    if ((CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 19.0.24215.1 AND
+         CMAKE_CXX_COMPILER_VERSION VERSION_LESS 19.10) OR
+       CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 19.10.25017)
+      set(CMAKE_CXX_STANDARD_DEFAULT 14)
+    elseif (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 16.0)
+      set(CMAKE_CXX_STANDARD_DEFAULT "")
+    else()
+      unset(CMAKE_CXX_STANDARD_DEFAULT)
+    endif()
   endif()
-endforeach()
-add_RunCMake_test(try_compile)
+  foreach(var
+      CMAKE_C_COMPILER_ID
+      CMAKE_C_COMPILER_VERSION
+      CMAKE_C_STANDARD_DEFAULT
+      CMAKE_CXX_COMPILER_ID
+      CMAKE_CXX_COMPILER_VERSION
+      CMAKE_CXX_STANDARD_DEFAULT
+      CMake_TEST_CUDA
+      )
+    if(DEFINED ${var})
+      list(APPEND try_compile_ARGS -D${var}=${${var}})
+    endif()
+  endforeach()
+  add_RunCMake_test(try_compile)
+endfunction()
+add_RunCMake_test_try_compile()
+
 add_RunCMake_test(try_run)
 add_RunCMake_test(set)
 add_RunCMake_test(variable_watch)