`--crate-type=rlib` + `-Cdebuginfo=2` + `-Zremap-cwd-prefix=.` is not reproducible on Windows

In https://github.com/rust-lang/rust/pull/128456#issuecomment-2289562440 we noticed that:

--crate-type=rlib + -C debuginfo=2 + -Z remap-cwd-prefix=. on Windows caused the rlib to be unreproducible.

https://github.com/rust-lang/rust/blob/0f442e265c165c0a78633bef98de18517815150c/tests/run-make/reproducible-build/Makefile#L4-L5

Two source files:

1. https://github.com/rust-lang/rust/blob/0ba9db87e61adcfd9a978188f61c20d9b423a099/tests/run-make/reproducible-build/reproducible-build-aux.rs
2. https://github.com/rust-lang/rust/blob/0ba9db87e61adcfd9a978188f61c20d9b423a099/tests/run-make/reproducible-build/reproducible-build.rs

Steps:

• Let "root" test directory be called $base_dir.
• rustc reproducible-build-aux.rs
• mkdir test
• cp reproducible-build.rs test/reproducible-build.rs
• compiler 1: rustc --crate-type=rlib -C debuginfo=2 -Zremap-cwd-prefix=. -L $cwd reproducible-build.rs
• mv libreproducible_build.rlib libfoo.rlib
• cd test
• compiler 2: rustc --crate-type=rlib -C debuginfo=2 -Zremap-cwd-prefix=. -L $base_dir --out-dir=$base_dir reproducible-build.rs
• cd $base_dir
• check if libreproducible_build.rlib and libfoo.rlib are different

Marking as S-needs-repro as I'm not sure of the root cause or exact reproduction environment; the test case failed on x86_64-msvc ci job. I'm also not exactly sure of the intended semantics of -Z remap-cwd-prefix=..

Start with tests/run-make/reproducible-build/Makefile and the two mentioned sources, reproducible-build-aux.rs and reproducible-build.rs. Reproduce the differing rlibs on the x86_64-msvc CI environment using the listed rustc commands, then investigate the intended semantics of -Z remap-cwd-prefix=.. Done means the Windows case has a confirmed root cause and an agreed reproducibility result.