FWIW, on my systems, every version of every package is installed in
its own prefix, even glibc. There are no /lib, /usr/lib, or
/usr/include - but "strings pkg-config" still includes those paths.
So those strings may not mean much.
I think the embedded path is used mostly to find the lib/pkgconfig
directory.
FWIW, setting PKG_CONFIG_PATH can mean yet another annoying change to
each app's build script.
If there is one toolchain associated with each lib/pkgconfig directory,
it might be more convenient for the users to plop a copy of
pkg-config into that toolchain's bin directory, with the right
default value for PKG_CONFIG_PATH. It's easier than teaching them
about PKG_CONFIG_PATH...