libgerbv.pc is used by the pkg-config tool to get information about the installed version of libgerbv. It should look something like this:

prefix=/usr/local
exec_prefix=${prefix}
libdir=${prefix}/lib
includedir=${prefix}/include
pkgincludedir=${prefix}/include/gerbv

Name: libgerbv
Description: Core library for gerbv
Requires: glib-2.0 gtk+-2.0
Version: 2.11.0
Libs: -L${libdir} -lgerbv
Cflags: -I${pkgincludedir}

The pkg-config tool can then extract the version of libgerbv by scanning through all the *.pc files on the computer. It works like this:

└──> pkg-config libgerbv --modversion
2.11.0

However, if the Version in that file is missing, it will report nothing.

The autotools programs use a configure script in order to configure a make file for building. (autotools is an older alternative to cmake.) One of the commands in the configure script might be like this:

PKG_CHECK_MODULES([gerbv], [libgerbv >= 2.1.0])

To check that the libgerbv version is at least 2.1.0.

However, if the libgerbv.pc file does not have a version, then it will fail and the user will be unable to complete configuration necessary for compilation.

By fixing libgerbv.pc, pkg-config will be able to report the correct version, and then configure will find that version and be able to create a makefile for programs that use libgerbv as a library.