tree-optimization/108482 - remove stray .LOOP_DIST_ALIAS calls

tree-optimization/108482 - remove stray .LOOP_DIST_ALIAS calls

The following deals with .LOOP_DIST_ALIAS surviving vectorization
because any of the loops involved were elided between loop distribution
and vectorization.  As opposed to .LOOP_VECTORIZED which exists only
between if-conversion and vectorization with no intermediate passes
this is more difficult to deal with in advance and thus cleaning
up after vectorization looks better.  There's the unconditional
vector lowering pass which looks like a good place for this (for
SIMD uid we have pass_simduid_cleanup).

	PR tree-optimization/108482
	* tree-vect-generic.cc (expand_vector_operations): Fold remaining
	.LOOP_DIST_ALIAS calls.

	* gcc.dg/torture/pr108482.c: New testcase.