When cross-compiling, it's common to have executables prefixed with
the name of the architecture you're building for,
e.g. aarch64-unknown-linux-musl-cc or x86_64-unknown-freebsd-pkg-config.
Lots of build tools support a PKG_CONFIG environment variable to
enable this use case.
With this change, I was able to successfully cross-compile and run
catgirl.
I avoided defaulting MANDIR to /usr/local/man because I thought it
didn't work on GNU/Linux and users would be confused, but it turns
out man-db's default configuration includes both /usr/local/man and
/usr/man, so ${PREFIX}/man is a sensical default.
June McEnroe
Alyssa Ross