[CMake] CMake misidentifies xlc++ as Clang

[Thompson, KT]

Hi,

I am using cmake-3.9.4 on a power9 system with CXX=xlc++ (IBM XL C++) and CMake is misidentifying the compiler as "clang".

% uname -a
Linux cn2021 4.11.0-44.4.1.el7a.ppc64le #1 SMP Sat Dec 9 02:17:51 EST 2017 ppc64le ppc64le ppc64le GNU/Linux

% echo $CXX
xlc++

% $CXX --version
IBM XL C/C++ for Linux, V13.1.6 (Community Edition)
Version: 13.01.0006.0001

% cmake ..
-- The CXX compiler identification is Clang 4.0.1
-- Check for working CXX compiler: /projects/opt/ppc64le/ibm/xlc-13.1.6/xlC/13.1.6/bin/xlc++
-- Check for working CXX compiler: /projects/opt/ppc64le/ibm/xlc-13.1.6/xlC/13.1.6/bin/xlc++ -- works
...

Because, the compiler_ID is misidentified, inappropriate compiler options are added when CXX_CXX_STANDARD is set (along with other issues).

Question 1: How do I report this as a bug? What additional information is needed to characterize the failure mode?

Question 2: Is there a way to force the compiler ID to be "XL" as a temporary work around until the bug is fixed?

Thank you,

-kt

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