checkLink: use C++ linker for checkLink if package sets self.cxx

PETSc will use the C++ linker in this case. This is needed when an
external library uses C++, but exports a C interface that we are
testing.
stylechecker: escape code portability
stylechecker: print line number
Merge branch 'jed/checklink-cxx' of bitbucket:petsc/petsc

* 'jed/checklink-cxx' of bitbucket:petsc/petsc:
  checkLink: use C++ linker for checkLink if package sets self.cxx
Merge branch 'blaise/stylecheck'

* blaise/stylecheck:
  stylechecker: print line number
  stylechecker: escape code portability