Auto merge of #131917 - jieyouxu:rmake-clang, r=Kobzol

Run the full stage 2 `run-make` test suite in `x86_64-gnu-debug`

Run the full `run-make` test suite in the `x86_64-gnu-debug` CI job. This is currently the *only* CI job where `//@ needs-force-clang-based-test` will be satisfied, so some `run-make` tests will literally never be run otherwise. Before this PR, the CI job only ran `run-make` tests which contains the substring `clang` in its test name, which is both (1) a footgun because it's very easy to forget and (2) it masks tests that would otherwise fail (even failing to compile) because the test is skipped if doesn't have a `clang` in its test name.

With the environment of `x86_64-gnu-debug`, two `run-make` tests failed before this PR:

1. `tests/run-make/issue-84395-lto-embed-bitcode/rmake.rs`: this was broken for a long time because `objcopy` in llvm bin tools was renamed to `llvm-objcopy`. This test was converted into a rmake.rs test, rather straight forward.
2. `tests/run-make/cross-lang-lto-riscv-abi/rmake.rs`: this was broken for a long time and never worked. The old version inspected human-readable output of `llvm-readobj --file-header` looking for substring `EF_RISCV_FLOAT_ABI_DOUBLE`, but the human-readable output will only contain something like `Flags: 0x5, RVC, double-float ABI`, hence it will never match. This test was fixed by instead using the `object` crate to actually decode the ELF headers looking for the specific `e_flags` based on reading the RISCV ELF psABI docs.

This PR is best reviewed commit-by-commit, two commits setup the support library for functionality and two commits are for each of the failing `run-make` tests.

I had to bump the `x86_64-gnu-debug` job to be ran with a runner with larger disk space.

Part of #132034.

try-job: x86_64-gnu-debug

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