[PATCH] compiletest: set the dylib path when gathering target cfg

[PATCH] compiletest: set the dylib path when gathering target cfg

If the compiler is built with `rpath = false`, then it won't find its
own libraries unless the library search path is set. We already do that
while running the actual compiletests, but #100260 added another rustc
command for getting the target cfg.

    Check compiletest suite=codegen mode=codegen (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
    thread 'main' panicked at 'error: failed to get cfg info from "[...]/build/x86_64-unknown-linux-gnu/stage1/bin/rustc"
    --- stdout

    --- stderr
    [...]/build/x86_64-unknown-linux-gnu/stage1/bin/rustc: error while loading shared libraries: librustc_driver-a2a76dc626cd02d2.so: cannot open shared object file: No such file or directory
    ', src/tools/compiletest/src/common.rs:476:13

Now the library path is set here as well, so it works without rpath.

FG: Context adapted

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
Gbp-Pq: Name u-make-compiletest-work-without-rpath.patch