Always set GOCACHE during build and let it point to pmbootstrap's work
dir. This has a similar effect as using ccache for C/C++.
Set GOMODCACHE conditionally: this is for caching the go modules (git
repositories) that get cloned during a build if they are not bundled
with the source. Usually APKBUILDs should cache them, but when using
pmbootstrap build --src, they would get downloaded over and over again.
Set GOMODCACHE automatically for --src and allow enabling/disabling this
manually with new --go-mod-cache / --no-go-mod-cache.
This speeds up multiple iterations of building the same package
significantly. I'm using it for:
$ pmbootstrap build postmarketos-mkinitfs --src=...
I've verified that using the same GOCACHE dir for multiple architectures
doesn't result in build artifacts for the wrong arch getting used.
Reviewed-by: Clayton Craft <clayton@craftyguy.net>
Link: https://lists.sr.ht/~postmarketos/pmbootstrap-devel/%3C20230223064743.1773-1-ollieparanoid@postmarketos.org%3E
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