PDAF-related change towards parallel build

[jjokella]

@kvrigor I am starting this as PDAF-related change to build on #89

• pdaf-compilations use $(MAKE) instead of make

• pdaf-compilations use -j ${PARALLEL_JOBS}

• split clean target to avoid race condition

• pdaf itself has been updated with some fixes aiming to ensure safe parallel compilation, which has so far worked TSMP-PDAF Makefiles: Fixes for ensuring safe parallel compilation pdaf#87

for testing / may be reverted

• relax CMake version condition
• add some make -> $(MAKE) replacements in eCLM externals (see eCLM branch master-parallel-build)

Compilation times eCLM-PDAF

Significant reduction that would be nice to have in the master

• ca. 11 minutes w/o parallel PDAF-compilation (but eCLM parallel as far as I understand)
• ca. 8 minutes with parallel PDAF-compilation (-j 16)

[kvrigor]

Thanks for the fixes @jjokella ! Just directly merge to parallel-build-mvh if everything works on your side. Review has been ongoing on that branch so we don't need to do review in this sub-PR.