Configure `--with-geany-libdir=$PREFIX/lib/x86_64-linux-gnu` and geany.pc is not found, checked and it is in `$PREFIX/lib/x86_64-linux-gnu/pkgconfig`

Have to set PKG_CONFIG_PATH to find it.

If geany and geany-plugins are built with libdir `$PREFIX/lib` and geany.pc in `$PREFIX/lib/pkgconfig` its found with no PKG_CONFIG_PATH needed.

@hyperair IIRC you were the instigator of `--with-geany-libdir` is this expected or broken?

Note: $PREFIX is some non-system prefix, yes I did spell it out in the commands.