`rust-lld` is using wrong zlib at runtime

After building rust 1.81.0 from sources, it configures with

-- Found ZLIB: /home/harmen/spack/opt/spack/linux-ubuntu23.10-zen2/clang-16.0.6/zlib-ng-2.1.6-xidpmzycb2jufhr6doa7anltbcyhu263/lib/libz.so (found version "1.3.0")

builds, and installs

<prefix>/lib/rustlib/x86_64-unknown-linux-gnu/bin/rust-lld

which lists

libz.so.1

among the DT_NEEDED libraries, but due to a lacking RPATH, at runtime the wrong libz.so.1 is used:

$ ldd lib/rustlib/x86_64-unknown-linux-gnu/bin/rust-lld | grep libz
	libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x000072120213b000)

This should have been the original zlib cmake has linked everything to.

Normally I would avoid this issue by passing -DCMAKE_INSTALL_RPATH_USE_LINK_PATH:BOOL=ON, but I don't see how I can pass this since rust's bootstrap script invokes cmake with a fixed set of arguments.

I noticed a related issue with binaries from https://static.rust-lang.org/dist/rust-1.81.0-x86_64-unknown-linux-gnu.tar.gz: both libLLVM.so.* and rust-lld depend on system libz.so, which makes the bootstrap binaries less self-contained than necessary.

Start by tracing the Rust bootstrap script's fixed CMake invocation and how it configures the installed rust-lld binary. Reproduce the issue with the Rust 1.81.0 source build, then use ldd on rust-lld to verify that runtime resolution selects the zlib used during the build rather than the system library.