toolchain: avoid broad substring replacement in get_toolchain_binary

[AayushMainali-Github]

Fixes #1636

Summary

Make get_toolchain_binary() only rewrite recognized linker suffixes instead of doing broad substring replacement on the whole linker filename.

Details

The old code chained .replace("ld", ...), .replace("gcc", ...), .replace("clang", ...), and .replace("cc", ...), which could rewrite unrelated parts of the linker name.

This changes the logic to only handle known endings:

• gcc
• clang
• cc
• ld

The existing ld.lld special case is kept.

[bjorn3]

As explained in #1636 (comment) I don't think this is worth it as it only gets used when CG_CLIF_FORCE_GNU_AS is set.