S/390: Rearrange fixuns_trunc pattern definitions.

S/390: Rearrange fixuns_trunc pattern definitions.

This reworks the fixuns_trunc* patterns a bit which got quite confusing
after adding z13 support.  Now we just have a single RTL standard name
expander definition ("fixuns_trunc<FP:mode><GPR:mode>2") which then
multiplexes to either the emulation variants *_emu or the hardware
implementations.

gcc/ChangeLog:

2017-03-24  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>

	* config/s390/s390.md
	("fixuns_truncdddi2", "fixuns_trunctddi2")
	("fixuns_trunc<BFP:mode><GPR:mode>2"): Merge into ...
	("fixuns_trunc<FP:mode><GPR:mode>2"): New expander.

	("fixuns_trunc<BFP:mode><GPR:mode>2", "fixuns_trunc<mode>si2"):
	Rename expanders to ...

	("fixuns_trunc<BFP:mode><GPR:mode>2_emu")
	("fixuns_truncdddi2_emu"): ... these.

	("fixuns_trunc<mode>si2_emu"): New expander.

	("*fixuns_truncdfdi2_z13"): Rename to ...
	("*fixuns_truncdfdi2_vx"): ... this.

From-SVN: r246451