Merge branch 'peter_fix_missing_file_test_gpu_vendor_agnostic_layerVariables_h' into 'master_pre_stage'

Add distcheck-gpu CI test and fix missing GPU source file in Makefile

See merge request !133

Allow 1 MPI rank for ELPA2

See merge request !132

fixed implicit function declaration for hip and cuda

See merge request !131

Removed all single-line if clauses

See merge request !130

Peter fix gpu copy tmatc

See merge request !129

fixed issue with multiple defenitions in cpp interface

See merge request !127

This QUICK fix, adds an forgotten free to remove a memory leak.
However, the GPU blas interfaces should be rewritten/cleaned up since
the malloc/free are not necessary. This requires touching all Fortran-C
GPU blas/solver/stream interfaces

Code fixes for nvhpcsdk

See merge request !125

configure.ac: Use a function prototype for _ linkage probing

The prototype chosen (char return type, no arguments) follows the
usual autoconf approach for link tests.  This is why compilers
are likely to continue to support this construct even if there is
a mismatch in types.

Future compilers are likely to reject implicit function declarations,
and the checks will always fail with such compilers.  (Implicit
function declarations were removed from C in 1999.)

Master pre stage

See merge request !124