d: vector float comparison doesn't result in 0 or -1 [PR108945]

When comparing two vectors, the type of vector was used as the result of
the condition result.  This meant that for floating point comparisons,
each value would either be `0.0' or `-1.0' reinterpreted as an integer,
not the expected integral bitmask values `0' and `-1'.

Instead, use the comparison type determined by truth_type_for as the
result of the comparison.  If a reinterpret is later required by the
final conversion for generating CmpExp, it is still only going to
reinterpret one integer kind as another.

	PR d/108945

gcc/d/ChangeLog:

	* d-codegen.cc (build_boolop): Evaluate vector comparison as
	the truth_type_for vector type.

gcc/testsuite/ChangeLog:

	* gdc.dg/pr108945.d: New test.