Bad, as explained before. Instead, how about adding some pkgconfig files
which are generated during build and thus we have complete control over their
contents? Eg. the attached one to xemacs-devel:
$ pkg-config xemacs --modversion
21.5.28
$ pkg-config xemacs --variable=sitestartdir
/usr/share/xemacs/site-packages/lisp/site-start.d
$ pkg-config xemacs --variable=sitepkglispdir
/usr/share/xemacs/site-packages/lisp
$ pkg-config xemacs --variable=sitemoduledir
/usr/lib64/xemacs/site-modules
$ pkg-config xemacs --cflags
-I/usr/lib64/xemacs-21.5-b28/x86_64-redhat-linux/include