From f969f1a9ce1d0045b9d056fd08c4683c34c420fa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C4=B0smail=20D=C3=B6nmez?= <ismail@i10z.com>
Date: Fri, 24 Nov 2017 13:22:46 +0100
Subject: Clang: Do not mistake clang-cl 6.0 for GNU-like clang

The check added by commit v3.10.0-rc2~2^2 (Clang: Diagnose unsupported
GNU-like clang targeting MSVC ABI, 2017-10-10) is incorrectly detecting
clang-cl 6.0 as GNU-like.  Currently cmake is testing if the clang
compiler accepts `--version` to see if it accepts GNU style flags.
However, with the latest llvm snapshot this also works for clang-cl:

    > clang-cl --version
    clang version 6.0.0 (trunk)
    Target: x86_64-pc-windows-msvc
    Thread model: posix
    InstalledDir: C:\Program Files\LLVM\bin

So instead we should use the `/?` flag which fails with clang but
works with clang-cl:

    > clang-cl /? &> /dev/null; echo $?
    0
    > clang /? &> /dev/null; echo $?
    1

Fixes: #17518
---
 Modules/CMakeDetermineCompilerId.cmake | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Modules/CMakeDetermineCompilerId.cmake b/Modules/CMakeDetermineCompilerId.cmake
index 347106e..15c304c 100644
--- a/Modules/CMakeDetermineCompilerId.cmake
+++ b/Modules/CMakeDetermineCompilerId.cmake
@@ -742,12 +742,12 @@ function(CMAKE_DIAGNOSE_UNSUPPORTED_CLANG lang envvar)
     return()
   endif()
 
-  # Test whether a GNU-like command-line option works.
-  execute_process(COMMAND "${CMAKE_${lang}_COMPILER}" --version
+  # Test whether an MSVC-like command-line option works.
+  execute_process(COMMAND "${CMAKE_${lang}_COMPILER}" /?
     RESULT_VARIABLE _clang_result
     OUTPUT_VARIABLE _clang_stdout
     ERROR_VARIABLE _clang_stderr)
-  if(NOT _clang_result EQUAL 0)
+  if(_clang_result EQUAL 0)
     return()
   endif()
 
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