+ The automatic check for the library path prefers the first directory
+ which currently exists. If none of the directories listed by
+ pkg-config exist, the check prefers a pkgconfig directory under the
+ "libdir" set by the configure script (which may not be the system
+ default), or if pkg-config lists nothing suitable, the first one which
+ is listed by pkg-config is used.
+
+ Automatic selection is overridden by providing an option-value
+ beginning with "/".
+
+ If this option is omitted, the default directory for installing
+ ".pc" files is ${libdir}/pkgconfig