libgcc is supposed to be built with the trace skip flags and branch
targets.  Add a zTPF header file fragment and add the -mtpf-trace-skip
option.

libgcc/ChangeLog:

2020-03-04  Andreas Krebbel  <krebbel@linux.ibm.com>

	* config.host: Include the new makefile fragment.
	* config/s390/t-tpf: New file.