testsuite/117958 - ifcombine differences on aarch64 vs rest

testsuite/117958 - ifcombine differences on aarch64 vs rest

ifcombine depends on BRANCH_COST and the testcase relies on ifcombine
to fully optimize the function.  But the important parts are optimized
everywhere, so the following delectively XFAILs the less important part.

	PR testsuite/117958
	* g++.dg/tree-ssa/pr117123.C: XFAIL parts on aarch64-*-*.