path solver: Default to global range if nothing found.

This has been a long time coming, but we weren't able to make the
change because of some unrelated regressions.

Tested on x86-64 & ppc64le Linux.

gcc/ChangeLog:

	* gimple-range-path.cc (path_range_query::internal_range_of_expr):
	Default to global range if nothing found.

gcc/testsuite/ChangeLog:

	* g++.dg/tree-ssa/pr31146-2.C: Add -fno-thread-jumps.