Better logging of problems in frontend.
Whenever we want to log a source code location,
we may not call FileLocation.getStartingLineNumber(),
but instead use the whole FileLocation object
(otherwise the error message is not helpful if multiple C files are
used).

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14302 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c