ldconfig: start of cleanup

Use bool.
Use local variables instead of static.
Remove non-functional debugging override of hints file path.
Use explicit exit() instead of return from main.
Minor style tweaks.

Reviewed by: emaste
Tested by: jbeich
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D33058