y sets LIBRARY_PATH which confuses gcc when compiling for a different target

[ds84182]

rustc_codegen_gcc/build_system/src/build.rs

Line 194 in fcac229

env.insert("LIBRARY_PATH".to_string(), gcc_path);

Linkers (both rust-lld and ld) attempt to link against the built GCC's crtbegin.o, which may not match the host architecture. Locally I've solved this by commenting out the LIBRARY_PATH environment variable then specifying RUSTFLAGS="-Lgcc-install/lib" to link against libgccjit.