Prefer bundled linker redux

Based on Windows bundle feedback we got to date, 
- We *do* want to prefer the bundled linker: The external one might be for the wrong architecture (e.g. 32 bit vs 64 bit).  On the other hand, binutils don't add many new features these days, so using an older bundled linker is not likely to be a problem.
- We *do* want to prefer bundled libraries: The external ones might not have the symbols we expect (e.g. what's needed for DWARF exceptions vs SjLj).  Since `-L rustlib/<triple>/lib` appears first on the linker command line, it's a good place to keep our platform libs that we want to be found first.

Closes #18325, closes #17726.