* include/lightning/jit_s390x.h, lib/jit_s390x-cpu.c,
lib/jit_s390x-fpu.c, lib/jit_s390x.c: New files
implementing the new s390x port.
* configure.ac, include/lightning.h,
include/lightning/Makefile.am,
include/lightning/jit_private.h,
lib/Makefile.am, lib/jit_disasm.c, lib/lightning.c:
Minor adaptation for the new s390x backend.
* check/float.tst: Update for the s390x result of
truncating +Inf to integer.
* check/qalu_mul.tst: Add extra test cases to better test
high word of signed multiplication as the result is
adjust from unsigned multiplication on s390x.
