Have liby and libcompat share *-dev and *-lib32_dev rules, and share
*-man rule for libcompat and libelftc. Also correct name substitution
and description for man rules.
Fixes: 5391bcf0f7e4 ("pkgbase: Do not record dependency on non-existent libcompat package")
Fixes: 65fa2fd23b9d ("pkgbase: Do record dependency on non-existent libelftc package")