[CMake] Finish off the clang-cl self host build

[zturner]

Summary

This allows clang-cl to self-host cleanly with no magic setup
steps required.

After this patch, all you have to do is set CC=CXX=clang-cl and
run cmake -G Ninja.

These changes only exist to support C++ features which are
unsupported in clang-cl, so regardless of whether the user
specifies they want to use them, we still have to disable them.

[rnk]

cmake/modules/AddLLVM.cmake

13

Won't 'NOT LLVM_EH_UNSUPPORTED' always be true? Normally it's undefined, but you set it to 0 in HandleLLVMOptions.

23

This should be under if(CLANG_CL) right? Otherwise gtest binaries can't recover from crashes and run the rest of the tests, which is semi-useful functionality.

cmake/modules/HandleLLVMOptions.cmake

31–32

I'm starting to feel like clang-cl should just silently ignore /Fd. Mind sending that patch instead? Otherwise, this needs a comment about /Fd.

[zturner]

Updated with suggestions. Also removed the unused arguments warning. I will make clang-cl ignore that argument silently in a separate patch.

[rnk]

lgtm

woot!`

cmake/modules/AddLLVM.cmake

25

Can you put something like # FIXME: Remove this when LLVM's SEH support is finished.?

cmake/modules/AddLLVM.cmake

 include(LLVMParseArguments)
 include(LLVMProcessSources)
 include(LLVM-Config)
 
 function(llvm_update_compile_flags name)
   get_property(sources TARGET ${name} PROPERTY SOURCES)
   if("${sources}" MATCHES "\\.c(;|$)")
     set(update_src_props ON)
   endif()
 
   # LLVM_REQUIRES_EH is an internal flag that individual
   # targets can use to force EH
-  if(LLVM_REQUIRES_EH OR LLVM_ENABLE_EH)
+  if((LLVM_REQUIRES_EH OR LLVM_ENABLE_EH) AND NOT CLANG_CL)
     if(NOT (LLVM_REQUIRES_RTTI OR LLVM_ENABLE_RTTI))
       message(AUTHOR_WARNING "Exception handling requires RTTI. Enabling RTTI for ${name}")
       set(LLVM_REQUIRES_RTTI ON)
     endif()
   else()
     if(LLVM_COMPILER_IS_GCC_COMPATIBLE)
       list(APPEND LLVM_COMPILE_FLAGS "-fno-exceptions")
     elseif(MSVC)
       list(APPEND LLVM_COMPILE_DEFINITIONS _HAS_EXCEPTIONS=0)
       list(APPEND LLVM_COMPILE_FLAGS "/EHs-c-")
     endif()
+    if (CLANG_CL)
+      list(APPEND LLVM_COMPILE_DEFINITIONS "GTEST_HAS_SEH=0")
+    endif()
   endif()
 
   # LLVM_REQUIRES_RTTI is an internal flag that individual
   # targets can use to force RTTI
   if(NOT (LLVM_REQUIRES_RTTI OR LLVM_ENABLE_RTTI))
     list(APPEND LLVM_COMPILE_DEFINITIONS GTEST_HAS_RTTI=0)
     if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
       list(APPEND LLVM_COMPILE_FLAGS "-fno-rtti")

cmake/modules/HandleLLVMOptions.cmake

elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
     if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 3.1)
       message(FATAL_ERROR "Host Clang version must be at least 3.1!")
     endif()
 
     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()
+      set(CLANG_CL 1)
     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")
       check_cxx_source_compiles("
 #include <atomic>
 std::atomic<float> x(0.0f);
 int main() { return (float)x; }"