Preserve environment variables in the makefile

[Luiz Felippe Santiago Rodrigues]

I think it would be useful a small change in the Makefile, so that it preserves some previously set environment variables (e.g. CFLAGS, F03FLAGS).

This minor change would allow the use of galacticus in a different build environments without touching its Makefile.

[Andrew Benson (abenson)]

I think this is an excellent idea. I wonder if this should be taken a step further though. For example, the Makefile currently overrides things like F03COMPILER. Changing:

F03COMPILER = gfortran

to

F03COMPILER ?= gfortran

might be good - this will only set F03COMPILER to gfortran if it isn't already set to something else in the environment.

Also, I've been thinking for a while that the "GALACTICUS_FLAGS" option is too blunt - it gets applied to F03FLAGS, CFLAGS AND CPPFLAGS, which can be problematic (or, at least, can cause warnings to be issued) if you put a Fortran specific comppiler option in GALACTICUS_FLAGS for example. So, perhaps it would be useful to have "GALACTICUS_F03FLAGS", "GALACTICUS_CFLAGS" and "GALACTICUS_CPPFLAGS"

[Andrew Benson (abenson)]

Here's a further patch which implements the suggestions from my previous comment. I also replaced F03FLAGS etc. with FCFLAGS which seems more conventional.

Any further changes needed? If not, I'll go ahead and merge this into the main branch.

[Luiz Felippe Santiago Rodrigues (luizfelippesr)]

I think this is great! It should be merged.

[Andrew Benson (abenson)]

OK - it's merged now. Thanks for the patch!