[ARM] Add -mbranch-cost option, and update a few tests

[ARM] Add -mbranch-cost option, and update a few tests

2018-01-10  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/
	* config/arm/arm.opt (-mbranch-cost): New option.
	* config/arm/arm.h (BRANCH_COST): Take arm_branch_cost into
	account.

	gcc/testsuite/
	* lib/target-supports.exp (check_effective_target_branch_cost):
	New function.
	* gcc.dg/builtin-bswap-7.c: Use branch_cost effective target.
	* gcc.dg/pr21643.c: Likewise.
	* gcc.dg/pr46309.c: Likewise.
	* gcc.dg/tree-ssa/phi-opt-11.c: Likewise.
	* gcc.dg/tree-ssa/phi-opt-2.c: Likewise.
	* gcc.dg/tree-ssa/reassoc-32.c: Likewise.
	* gcc.dg/tree-ssa/reassoc-33.c: Likewise.
	* gcc.dg/tree-ssa/reassoc-34.c: Likewise.
	* gcc.dg/tree-ssa/reassoc-35.c: Likewise.
	* gcc.dg/tree-ssa/reassoc-36.c: Likewise.
	* gcc.dg/tree-ssa/ssa-ifcombine-13.c: Likewise.
	* gcc.dg/tree-ssa/ssa-ifcombine-ccmp-1.c: Likewise.
	* gcc.dg/tree-ssa/ssa-ifcombine-ccmp-2.c: Likewise.
	* gcc.dg/tree-ssa/ssa-ifcombine-ccmp-3.c: Likewise.
	* gcc.dg/tree-ssa/ssa-ifcombine-ccmp-4.c: Likewise.
	* gcc.dg/tree-ssa/ssa-ifcombine-ccmp-5.c: Likewise.
	* gcc.dg/tree-ssa/ssa-ifcombine-ccmp-6.c: Likewise.

From-SVN: r256434