Inherit `$(MAKE)` during install

[zbeekman]

See https://github.com/radiasoft/container-beamsim-part1/issues/2#issuecomment-414017341 for additional context

[khsa1]

Could you give some more information about expected behavior?

[zbeekman]

I'm not sure how feasible/urgent this is... basically a user was expecting running make ... install to use the number of processes set by make, not every available system process... Also, I think they launched the installation from a makefile of their own.

To be fair, the threading/processes requested can be a bit aggressive on a shared login node, so a switch or similar to explicitly control how many threads/processes to use for compilation of TAU and other libraries could be nice. Then the makefile could be edited to pass the inherited number of processes passed by the user (any recursive invocation of make should use $(MAKE) to inherit flags, etc.). But it looks like the installer hands off to python which is spooling jobs & threads for the build. We would explicitly have to fetch the number of jobs passed to make -j <N> install ... with something like https://stackoverflow.com/questions/5303553/gnu-make-extracting-argument-to-j-within-makefile which is a but ugly, IMO.