/usr/lib/pkgconfig/igraph.pc is in libigraph0-dev 0.5.4-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 | prefix=/usr
exec_prefix=${prefix}
libdir=${exec_prefix}/lib
includedir=${prefix}/include
Name: libigraph
Description: A library for creating and manipulating graphs
Version: 0.5.4
Libs: -L${libdir} -ligraph
Cflags: -I${includedir}
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