Always patch the interpreter of rustlib binaries

[marienz]

When using stable.toolchain,
lib/rustlib/x86_64-unknown-linux-gnu/bin/rust-lld and other binaries in the same directory are not patched, so they do not work. I'm not sure exactly when Rust uses these, but it seems to break cross-compilation to wasm32-unknown-unknown.

Fix it by generalizing the patching applied to the rustc component. Replace the glob with a find invocation to avoid errors on components that have a lib directory but no lib/rustlib/*/bin.

[marienz]

The diff doesn't make it obvious what I'm actually changing: I'm swapping two loops and making a small change to one of them, but the loop body is sufficiently similar the diff looks like I'm modifying two loops. The change should be:

• The code starting at line 47 in the old version should match line 56 in the new version.
• The code starting at line 59 in the old version moves to line 46 in the new version. The find we're looping over changes, but the patchelf invocation is unchanged.

I think you can test this by manually running lib/rustlib/x86_64-unknown-linux-gnu/bin/rust-lld --version from a stable toolchain (should crash before this change, print lld is a generic driver. after). Let me know if I need to put together a proper reproducer: I have a local project that doesn't work without this and does with, but it's a bit of a mess (multiple crates and cross-compilation to multiple platforms).

[stillinbeta]

(disregard previous message, I can't read error messages)

I can confirm this has solved the rust-lld issue for me!

[SandWoodJones]

Can also confirm this

[eureka-cpu]

I wonder if this is at all related to #206, both having to do with CC linker issues. Will need to do a bit of testing here. Thanks @marienz.

EDIT: Also please target staging.

[marienz]

Rebased to staging (sorry, must've missed that at the bottom of README before), but although the change is likely still correct I can't conveniently test it anymore (I've migrated off fenix in the >1y since I sent this). So please confirm this still fixes things before merging...