rely on pkg-config when finding check
rely on pkg-config when finding check

The former code complains to install check even it is actually
installed.

PKRoma/xrdp,neutrinolabs/xrdp,PKRoma/xrdp,metalefty/xrdp,neutrinolabs/xrdp,metalefty/xrdp,PKRoma/xrdp,neutrinolabs/xrdp,metalefty/xrdp