Improve -Wuninitialized note location.

Improve -Wuninitialized note location.

Related:
PR tree-optimization/17506 - warning about uninitialized variable points to wrong location
PR testsuite/37182 - Revision 139286 caused gcc.dg/pr17506.c and gcc.dg/uninit-15.c

gcc/ChangeLog:

	PR tree-optimization/17506
	PR testsuite/37182
	* tree-ssa-uninit.c (warn_uninit): Remove conditional guarding note.

gcc/testsuite/ChangeLog:

	PR tree-optimization/17506
	PR testsuite/37182
	* gcc.dg/diagnostic-tree-expr-ranges-2.c: Add expected output.
	* gcc.dg/uninit-15-O0.c: Remove xfail.
	* gcc.dg/uninit-15.c: Same.