middle-end: Add new tbranch optab to add support for bit-test-and-branch operations

This adds a new test-and-branch optab that can be used to do a conditional test
of a bit and branch.   This is similar to the cbranch optab but instead can
test any arbitrary bit inside the register.

This patch recognizes boolean comparisons and single bit mask tests.

gcc/ChangeLog:

	* dojump.cc (do_jump): Pass along value.
	(do_jump_by_parts_greater_rtx): Likewise.
	(do_jump_by_parts_zero_rtx): Likewise.
	(do_jump_by_parts_equality_rtx): Likewise.
	(do_compare_rtx_and_jump): Likewise.
	(do_compare_and_jump): Likewise.
	* dojump.h (do_compare_rtx_and_jump): New.
	* optabs.cc (emit_cmp_and_jump_insn_1): Refactor to take optab to check.
	(validate_test_and_branch): New.
	(emit_cmp_and_jump_insns): Optiobally take a value, and when value is
	supplied then check if it's suitable for tbranch.
	* optabs.def (tbranch_eq$a4, tbranch_ne$a4): New.
	* doc/md.texi (tbranch_@var{op}@var{mode}4): Document it.
	* optabs.h (emit_cmp_and_jump_insns): New.
	* tree.h (tree_zero_one_valued_p): New.