Fix parallel builds with GNU make

[joseeroman]

In order for make -j to work correctly, the BLACS library should be built before the other libraries. This can be achieved with an explicit dependency.

Also, the child make processes must be launched with $(MAKE) so that the -j option is propagated correctly.

[weslleyspereira]

Thanks for highlighting this issue! I think a better fix would be to make sure all dependencies on BLACS are well established on the Makefile. What do you think?

[joseeroman]

Yes, that could be an alternative solution. I proposed this solution because I am not sure if BLACS is the only dependency or there are other dependencies between the prerequisites of the lib target. You know better than me.

[joseeroman]

I have modified the commit. Assuming that BLACS is the only dependency, the new version should work equally well, and does not contain any GNU-specific keywords.

[joseeroman]

Note that the current version fixes make -j lib but not the all target. The previous solution was good for both. To me, this is not important.

[weslleyspereira]

Thanks! Even if it does not solve the whole problem with the dependencies, I believe this is the right way to go.

Since those changes solve your problem, I will approve this PR. I will open a new issue so as we do not forget to fix the dependencies.

Thanks!