arm: Fix uaddvdi4 expander [PR93494]

arm: Fix uaddvdi4 expander [PR93494]

uaddvdi4 expander has an optimization for the low 32-bits of the 2nd input
operand known to be 0.  Unfortunately, in that case it only emits copying of
the low 32 bits to the low 32 bits of the destination, but doesn't emit the
addition with overflow detection for the high 64 bits.
Well, to be precise, it emits it, but into an RTL sequence returned by
gen_uaddvsi4, but that sequence isn't emitted anywhere.

2020-01-30  Jakub Jelinek  <jakub@redhat.com>

	PR target/93494
	* config/arm/arm.md (uaddvdi4): Actually emit what gen_uaddvsi4
	returned.

	* gcc.c-torture/execute/pr93494.c: New test.