Rollup merge of #106811 - khuey:dwp_extension, r=davidtwco

Append .dwp to the binary filename instead of replacing the existing extension.

gdb et al. expect to find the dwp file at `<binary>`.dwp, even if <binary> already has an extension (e.g. libfoo.so's dwp is expected to be at libfoo.so.dwp).

diff --cc compiler/rustc_codegen_ssa/src/back/link.rs
Simple merge