CUDA enabled configure script

This merge request allows to generate the make.inc file for CUDA compilation with autotools and provides an automatic building system for the external GPU libraries.

Changes:

• Minimal version for autotools increased from 2.60 to 2.64.

New features:

• A modified configure script that features three new parameters: --with-cuda, --with-cuda-cc, --with-cuda-runtime, described by ./configure --help. The configure script checks that:

• PGI compilers are used.

• nvcc is available.

• Currently needed libraries for the envisaged porting are present.

• The configure script generates a new make.inc that defines the flag __CUDA and embeds all the details about the CUDA configuration i.e.:

• CUDA_RUNTIME: CUDA runtime currently in use.

• CUDA_CC: compute capabilities to be used in code generation.

• CUDA_EXTLIBS: external libraries to be configured and generated. Currently only the eigensolver.

• CUDA_LIBS: libraries to be used at linking time (PGI libraries and external packages)

• A modified extlibs_makefile that automatically downloads and generate this eigevsolver.

• A small C code and a python wrapper that can be used to simplify the building process for the user and/or the debugging phase. The C code dumps the details of the GPUs in a yaml file (device_propc.c). The Python script collects these information and generate a draft for the configure line.

To be done/discussed before merging:

• If/where/how to document the new configure options: for the developers? For the users?
• Align .gitlab-ci.yaml to standard QEF CI.

Known problems:

What follows is a general problem that becomes particularly relevant when building with the PGI compilers. When setting the flag -Mlarge_arrays in make.inc, this flag is not propagated to the libraries generated by extlibs_makefile. This is especially problematic for the FoX library, that fails while reading the pseudopotentials for this reason. As a consequence, -Mlarge_arrays is not currently set in the configure, but will be needed in the future (for large allocations). A solution to the problem of propagating flags to external libraries build system must be found.