/usr/share/pkgconfig/glm.pc is in libglm-dev 0.9.9~a2-2.
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 | prefix=/usr
includedir=${prefix}/include
Name: GLM
Description: OpenGL Mathematics
Version: 0.9.9
Cflags: -I${includedir}
|