Simplify link flags in configure

[gassmoeller]

A suggestion for how to simplify the link options in the configure script. This should be carefully tested on systems with:

• Intel compiler + MKL
• GNU compiler without MKL (this worked on my system)
• GNU compiler with MKL through debian apt
• GNU compiler with MKL through conda
• GNU compiler on MacOS with MKL through conda

[illorenzo7]

I at least tested this on Pleiades (intel + mkl) and it fixed my issue with the "$MKL_LIB" appearing in configure instead of "-mkl". (So it now compiles with this fix).

[feathern]

I just tested the GNU compiler with and without MKL (using Openblas through conda). This worked fine for me.

[feathern]

I also just tested the GNU compiler with MKL installed via apt. No problems there either.

[cianwilson]

I tested this on an intel mac (OS Ventura 13.6.7) using:

conda config --set channel_priority strict
conda env create -f environment.yml
conda activate radev
conda install mkl
export MKLROOT=$CONDA_PREFIX
./configure --FC=mpifort --CC=gcc -conda-mkl
make
make install

which produced a functioning executable (tested on an input_example) despite an ld warning:

ld: warning: object file (cmkdir.o) was built for newer macOS version (13.0) than being linked (11.5)

[gassmoeller]

So that seems pretty good then.

ld: warning: object file (cmkdir.o) was built for newer macOS version (13.0) than being linked (11.5)

Hmm, I cannot see how my change could have affected that, the flags for Macos should be exactly as before. Can you check if setting STD_FLAGS='-lc++' in the lines above resolves the warning? Then it would be related to #532 and not this one.

[feathern]

This looks good. We just checked and there was no linking against the standard C++ library. I'm merging.