Provide support for using valgrind with PETSc on the Apple MacOS, all tests pass

Turn off opencl support for MPICH if running on Apple MacOS with valgrind,
   because the check in hwloc() crashes under valgrind
Turn off lazy dynamic loading of shared libraries with valgrind, because that crashes valgrind
Provide custom mkdtemp() with valgrind because Apple's system one is not supported by valgrind
Add Apple specific suppression files for valgrind
Update documentation for using valgrind with Apple
Warn user they must use --download-fblaslapack or --download-f2cblaslapack with valgrind

Commit-type: portability-fix
/spend 6h
Reported-by: Hapla Vaclav <vaclav.hapla@erdw.ethz.ch>
Thanks-to: Hong Zhang hongzhang@anl.gov