Check that Fortran sources run; Robust Fortran features

[perazz]

This PR enables fpm to perform checks on supported Fortran features at project build time, with the aim to improve/enable Fortran features support.

• implement, test a check_fortran_source_runs compiler property to run Fortran sources on-the-fly, similar to CMake's CheckFortranSourceRuns
• implement with_qp fortran feature that checks for quad-precision real kind support
• implement with_xdp fortran feature that checks for 80-bit extended-precision real kind support

Later, I plan to add conditional fortran features quad-precision and extended-precision to the fortran table. We should decide on a suitable logic: automated setting of preprocessor flags such as WITH_QP and WITH_XDP every time? or just if required in the fortran table? etc.

Context:
#864
fortran-lang/stdlib#821
cc: @jvdp1 @jalvesz @awvwgk @fortran-lang/fpm @fortran-lang/stdlib

[perazz]

Will merge soon as there are no comments. Thanks.

[jalvesz]

Hi @perazz I wanted to ask something before and got busy in between, sorry.

We should decide on a suitable logic: automated setting of preprocessor flags such as WITH_QP and WITH_XDP every time? or just if required in the fortran table?

Here, should it be understood that setting the option in the fortran table would be equivalent to adding a macro option under preprocessor.cpp ['-DWITH_QP'] for instance? in the sense that one should not need to added by hand? If that is the case LGTM. I did not fully understood the alternative.

[perazz]

Thanks @jalvesz, the current PR does not address that yet as it just builds the internal capability to check that the current compiler supports qp and xdp by compiling and running a small program.
That is exactly the aim I would like to address further in a separate PR. I think the options are:

• Always generate standardized macros when those features are supported -> I'm very much in favor at least for these ones, WITH_QP, WITH_XDP, WITH_MPI, etc. so that conditional programming is always enabled, and that also consolidates standardized macros from fpm

• Add these as mandatory features in the fortran table. In other words, if one package may require a specific precision to be supported

[fortran]
quadruple-precision=true

and fpm can check whether that is supported by the current compiler, and stop if it is not the case.

[jalvesz]

Cristal clear! thanks!

[henilp105]

Thanks @perazz , Looks good to me!