* configure.ac: Don't ignore user-provided LDFLAGS while trying
   to detect libmagic. Fixes libmagic detection where configure
   relies on LDFLAGS to find libraries in non-standard locations.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1577200 13f79535-47bb-0310-9956-ffa450edef68