newTempName: instead of bumping the processId until we find a name
that isn't used, add an integer suffix to the processId.  This should
prevent temp-file conflicts that appear to have been affecting our
nightly builds and occasionally make -j.

The right way to allocate a temporary file is to create it straight
away, but I'm not sure of the implications of passing existing
temporary files to the various sub-processes that GHC executes, hence
this fix instead.