Detect cross compilation and adjust Cargo output directory

[alerque]

Cross compiling with Cargo adds a segment to the output directory with the host info. Currently we don't have a way to detect this and adjust, we just blindly assume the Cargo directory will be "target/release" instead of perhaps "target/x86_64-unknown-linux-gnu/release".

This is a problem for some distro packages, e.g. Void bumped into this.

Somehow we should detect whether cross compilation is being used and what the target triple is.

[alerque]

@Luciogi Any hints on how Void's build system is initializing cross compilation? Are you using the --host <target> configure option or env vars or what?

I think what I did in #2178 will address this by always building into a target directory with the target triple specified, hence not needing the patch you setup. But I'm not 100% sure this will cover all cases. I'd be happy to test some more if I know more about the scenarios where this is an issue.

[Luciogi]

I am not completely familiar with xbps-src internal functions.
Following will be my guess.

sile - template uses

build-style=gnu-configure
build-helper=rust

as problem is with rust output binary location,
xbps-src loads this script before compiling
https://github.com/void-linux/void-packages/blob/master/common/build-helper/rust.sh
https://github.com/void-linux/void-packages/blob/master/common/build-style/gnu-configure.sh

[alerque]

Thanks for the extra information. Given what I see in those scripts I think the fix I added for this is going to work. You could cherry-pick it into the v0.15.6 sources and see if the build works after removing your work around, or just wait for v0.15.7 too see if the workaround can be removed. If not I'm happy to look into this farther.