middle-end: check for vector mode before calling get_mask_mode [PR116074]

middle-end: check for vector mode before calling get_mask_mode [PR116074]

For historical reasons AArch64 has TI mode vector types but does not consider
TImode a vector mode.

What's happening in the PR is that get_vectype_for_scalar_type is returning
vector(1) TImode for a TImode scalar.  This then fails when we call
targetm.vectorize.get_mask_mode (vecmode).exists (&) on the TYPE_MODE.

This checks for vector mode before using the results of
get_vectype_for_scalar_type.

gcc/ChangeLog:

	PR target/116074
	* tree-vect-patterns.cc (vect_recog_cond_store_pattern): Check vector mode.

gcc/testsuite/ChangeLog:

	PR target/116074
	* g++.target/aarch64/pr116074.C: New test.