> Does /mingw/bin exist, and if so, is there anything in it?

Yes, /mingw is mapped to my MinGw installation path (C:\bin\mingw) so /mingw/bin contains the MinGW binaries.

> How about /c/Devel/emacs/build/bin?

Yes, /c/Devel/emacs/build is where I put all additional binaries and libraries required (the -c and -L args in my configure.sh command use c:/Devel/emacs/include and c:/Devel/emacs/lib instead of c:/Devel/emacs/build/{include,lib} because I have symlinks).

> In general, the MinGW's bin directory should be _after_ the MSYS
> directories on PATH, otherwise you risk invoking native MinGW programs
> instead of their MSYS name-sakes.

I'll fix that.