[Pre-RFC] target-glibc: Proposal to add native support for GLIBC versions for the -gnu targets

Are there plans on making the tool that does the "local glibc -> stub library" standalone? I can forsee this being very useful even outside of Rust.

This is quite a trivial task. A standalone binary may either automatically download the required glibc version sources or use whatever sources the user provides (not from the linked libc.so.6 on your system).

Would a linker script be easier (it may well might not be, but I'm curious if it was considered)?

Linker script is generated/used under the hood anyway. It can be preserved next to the generated stub libraries.

Also, has an equivalent for libstdc++ and/or libc++ been considered?

No. This is way outside of the scope of this RFC. Moreover, I do not know of any success stories involving libstdc++/libc++ from languages other than C++. If it were possible with reasonable effort, Rust could automatically use libraries that expose API as C++ classes with std::* types. In other words, why would you even need something like that?