mk: fix unnecessary library relinking with incremental builds

[val_packett.cool]

Summary

Initial libs such as csu are always built (.PHONY), and their installation
to WORLDTMP was causing all the subsequent libraries to be considered out-of-date
even when in reality they were not. Use install -C more consistently everywhere
to avoid unnecessarily updating the mtimes in WORLDTMP, fixing this problem.

This cut down my no-change buildworld time from 30 to 15 seconds.

Fixes: https://lists.freebsd.org/pipermail/freebsd-current/2016-May/061481.html TODO.1
Sponsored by: https://www.patreon.com/valpackett

Test Plan

I… don't think install -C could ever cause problems? But please do test various build configurations with this.

[sjg]

Seems reasonable

[freebsd_igalic.co]

In D39980#910253, @sjg wrote:

Seems reasonable

wanna commit this?

[diizzy]

@sjg Friendly ping, might be nice to get this in before 14-CURRENT branching?

[jrtc27]

I don't think this is specific to WITH_META_MODE?

[val_packett.cool]

Well, you wouldn't really save any time on a non-incremental build as all the libraries would be rebuilt anyway. The *problem* this solves is specific to META_MODE :)

[jrtc27]

In D39980#938622, @val_packett.cool wrote:

Well, you wouldn't really save any time on a non-incremental build as all the libraries would be rebuilt anyway. The *problem* this solves is specific to META_MODE :)

WITHOUT_META_MODE builds can be incremental. That's what WITHOUT_CLEAN is for, which people widely use so as to not waste time.

[val_packett.cool]

WITHOUT_CLEAN builds should benefit as well then.. (Not sure why people still use it when META_MODE exists but okay :D)

I guess the commit title should just mention "incremental builds".

[freebsd_igalic.co]

In D39980#938624, @val_packett.cool wrote:

WITHOUT_CLEAN builds should benefit as well then.. (Not sure why people still use it when META_MODE exists but okay :D)

for one, because you don't need to load a special module for it to work.

this has the added advantage of it working in cross build situations.