add macro to assist in checking if code snippets compile

[white238]

We ran into a problem where Umpire was trying to use CMake's macro check_cxx_source_compiles. We found that it did not honor the CMAKE_CXX_STANDARD. There is a policy to control this but I could only get it to work for CMake 3.14.5 and 3.18.0 but anything above that did not work.

This adds a macro we have used in Axom for a while. It is much more reliable and also allows you to output verbosely to the screen. For example:

-- [blt_check_code_compiles] Attempting to compile source string: 
#include <iostream>

  int main(int, char**)
  {

    std::cout << "Hello World!" << std::endl;

    return 0;
  }
-- [blt_check_code_compiles] Compiler output: 
Change Dir: /usr/WS2/white238/blt/repo/tests/internal/build/unit/CMakeTmp/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/gmake -f Makefile cmTC_5e24b/fast && /usr/bin/gmake  -f CMakeFiles/cmTC_5e24b.dir/build.make CMakeFiles/cmTC_5e24b.dir/build
gmake[1]: Entering directory `/usr/WS2/white238/blt/repo/tests/internal/build/unit/CMakeTmp/CMakeFiles/CMakeTmp'
Building CXX object CMakeFiles/cmTC_5e24b.dir/_bltCheckCompilesykiyL.cpp.o
/usr/tce/packages/gcc/gcc-10.2.1/bin/c++   -Wall -Wextra       -fPIE -std=c++11 -o CMakeFiles/cmTC_5e24b.dir/_bltCheckCompilesykiyL.cpp.o -c /usr/WS2/white238/blt/repo/tests/internal/build/unit/_bltCheckCompilesykiyL.cpp
Linking CXX executable cmTC_5e24b
/usr/tce/packages/cmake/cmake-3.20.2/bin/cmake -E cmake_link_script CMakeFiles/cmTC_5e24b.dir/link.txt --verbose=1
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gmake[1]: Leaving directory `/usr/WS2/white238/blt/repo/tests/internal/build/unit/CMakeTmp/CMakeFiles/CMakeTmp'



-- [blt_check_code_compiles] The code snippet successfully compiled

[mcfadden8]

This looks great @white238 - I tried out the branch locally with my Umpire tests and all seems good.

[eugeneswalker]

This looks great @white238 - I tried out the branch locally with my Umpire tests and all seems good.

This fixes spack/spack#32932 for me

[kennyweiss]

Thanks @white238 !

[kennyweiss]

Suggestion: Should we use a "bracket argument" (multiline string) instead of a single quote string?
One benefit would be that we wouldn't need to modify the quotation marks
e,g,:

[=[
#include <iostream>

int main(int, char**)
{
    std::cout << \"Hello World!\" << std::endl;
    return 0;
}
]=]

See: https://cmake.org/cmake/help/latest/manual/cmake-language.7.html#bracket-argument

[white238]

This worked.. added it as a code snippet in the documentation as well.

[kennyweiss]

Does SOURCE_STRING need to be a multiValueArg because it can have embedded semicolons?

[white238]

i bet it shouldn't actually.

[white238]

Tried changing this to a single value arg and it removed all the semi-colons.

[white238]

https://llnl-blt.readthedocs.io/en/feature-white238-add_try_compile/api/utility.html#blt-check-code-compiles