Move $__RootfsDir/{system/boot,} on Haiku

[am11]

This is needed to unblock dotnet/dotnet-buildtools-prereqs-docker#669, which requires bin/ directory at the root or rootfs dir.

[am11]

cc @jessicah @trungnt2910

[jessicah]

This change will not work as-is, unless invocations of the compilers specifies the sysroot explicitly, but there are no binaries in that location.

The files under $__RootfsDir/system/boot is basically just the libraries and headers. The cross-compiler is under $__RootfsDir/generated/cross-tools-x86_64. So you'd need to update $PATH. Alternatively, perhaps symlinks might work? The build system doesn't currently support them being elsewhere, I'd need to modify Haiku's configure script to achieve that.

The path that files are extracted to are configured in the cross-compiler when configuring the Haiku repo, https://github.com/dotnet/arcade/blob/main/eng/common/cross/build-rootfs.sh#L438, which eventually arrives at https://github.com/haiku/haiku/blob/master/build/scripts/build_cross_tools_gcc4#L203.

[am11]

Thanks. I don't have your Haiku changes for dotnet/runtime so I was relying on manual / dryrun testing. The validation which is failing downstream is: https://github.com/dotnet/dotnet-buildtools-prereqs-docker/blob/99143ac0c21d525ad62dab9c258993681221f7b8/src/ubuntu/build-scripts/build-rootfs.sh#L64, but it turned out we already have a way to override rootfsBinDirArg. I will close this and use that (it is just a sanity check which looks for sentinel file/folder, it doesn't actually validate if the compile binaries work).