Audit MSVC references in cmake files to consider clang++ (google#1669)

There are three major compilers on Windows targeting the MSVC ABI (i.e.
linking with microsofts STL etc.):
  - `MSVC`
  - `clang-cl` aka clang with the MSVC compatible CLI
  - `clang++` aka clang with gcc compatible CLI

The cmake variable `MSVC` is only set for the first two as it defined in
terms of the CLI interface provided:

> Set to true when the compiler is some version of Microsoft Visual
> C++ or another compiler simulating the Visual C++ cl command-line syntax.

(from cmake docs)

For many of the tests in the library its the ABI that matters not the
cmdline, so check `CMAKE_CXX_SIMULATE_ID` too, if it is `MSVC` the
current compiler is targeting the MSVC ABI. This handles `clang++`

Author: Maetveis

AUTHORS

@@ -31,6 +31,7 @@ Evgeny Safronov <division494@gmail.com>
 Fabien Pichot <pichot.fabien@gmail.com>
 Federico Ficarelli <federico.ficarelli@gmail.com>
 Felix Homann <linuxaudio@showlabor.de>
+Gergely Meszaros <maetveis@gmail.com>
 Gergő Szitár <szitar.gergo@gmail.com>
 Google Inc.
 Henrique Bucher <hbucher@gmail.com>

CMakeLists.txt

@@ -21,7 +21,7 @@ if(BENCHMARK_FORCE_WERROR)
   set(BENCHMARK_ENABLE_WERROR ON)
 endif(BENCHMARK_FORCE_WERROR)
 
-if(NOT MSVC)
+if(NOT (MSVC OR CMAKE_CXX_SIMULATE_ID STREQUAL "MSVC"))
   option(BENCHMARK_BUILD_32_BITS "Build a 32 bit version of the library." OFF)
 else()
   set(BENCHMARK_BUILD_32_BITS OFF CACHE BOOL "Build a 32 bit version of the library - unsupported when using MSVC)" FORCE)
@@ -45,7 +45,7 @@ option(BENCHMARK_ENABLE_LIBPFM "Enable performance counters provided by libpfm"
 set(CMAKE_CXX_VISIBILITY_PRESET hidden)
 set(CMAKE_VISIBILITY_INLINES_HIDDEN ON)
 
-if(MSVC)
+if(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
     # As of CMake 3.18, CMAKE_SYSTEM_PROCESSOR is not set properly for MSVC and
     # cross-compilation (e.g. Host=x86_64, target=aarch64) requires using the
     # undocumented, but working variable.
@@ -66,7 +66,7 @@ function(should_enable_assembly_tests)
       return()
     endif()
   endif()
-  if (MSVC)
+  if (MSVC OR CMAKE_CXX_SIMULATE_ID STREQUAL "MSVC")
     return()
   elseif(NOT CMAKE_SYSTEM_PROCESSOR MATCHES "x86_64")
     return()
@@ -128,7 +128,7 @@ if (BENCHMARK_BUILD_32_BITS)
   add_required_cxx_compiler_flag(-m32)
 endif()
 
-if (MSVC)
+if (MSVC OR CMAKE_CXX_SIMULATE_ID STREQUAL "MSVC")
   set(BENCHMARK_CXX_STANDARD 14)
 else()
   set(BENCHMARK_CXX_STANDARD 11)

CONTRIBUTORS

@@ -51,6 +51,7 @@ Fanbo Meng <fanbo.meng@ibm.com>
 Federico Ficarelli <federico.ficarelli@gmail.com>
 Felix Homann <linuxaudio@showlabor.de>
 Geoffrey Martin-Noble <gcmn@google.com> <gmngeoffrey@gmail.com>
+Gergely Meszaros <maetveis@gmail.com>
 Gergő Szitár <szitar.gergo@gmail.com>
 Hannes Hauswedell <h2@fsfe.org>
 Henrique Bucher <hbucher@gmail.com>

test/CMakeLists.txt

@@ -183,7 +183,7 @@ compile_output_test(memory_manager_test)
 add_test(NAME memory_manager_test COMMAND memory_manager_test --benchmark_min_time=0.01s)
 
 # MSVC does not allow to set the language standard to C++98/03.
-if(NOT CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
+if(NOT (MSVC OR CMAKE_CXX_SIMULATE_ID STREQUAL "MSVC"))
   compile_benchmark_test(cxx03_test)
   set_target_properties(cxx03_test
       PROPERTIES