Reorder PIO to occur before NetCDF in common.mk

[billsacks]

This is needed with the linker on cygwin since PIO uses NetCDF, so the link flags need to be ordered -lpioc -lnetcdf. (It's possible that other linkers need this also, though we haven't seen the need for it on our test systems.)

This replaces #348 , based on decided-upon solution from this week's ESMF core team meeting.

FYI @theurich @danrosen25 @harmenwierenga

@harmenwierenga - I took your commit from your earlier branch that reorders the PIO and NETCDF sections in common.mk, because after further discussion, we saw rationale for that approach.

@theurich and @danrosen25 - let me know if you'd like to look this over before I merge it.

[DWesl]

Since this is based on environment variables rather than attempted compilation, this should work fine

It's possible that other linkers need this also, though we haven't seen the need for it on our test systems

Windows is the only other system I've noticed with that link-order requirement, though it seems to be weaker: there's another project that probably had Windows CI that apparently handled -lblas -llapack just fine before I reversed the order so it would compile on Cygwin.

I'm told there's a -no-undefined linker flag that should emulate some of the Windows linker semantics, but I don't know which compiler supports it nor how much of the Windows semantics it implements.

[theurich]

Looks good to me. Thanks!

[harmenwierenga]

@billsacks Thank you for this! I have not had time to look into testing it unfortunately. PIO accepted my changes to their repo a while ago, would it be feasible to update the version of PIO that is used by ESMF?

[DWesl]

would it be feasible to update the version of PIO that is used by ESMF?

Like #359?

[harmenwierenga]

Nice, thank you!