RISC-V: Enable pressure-aware scheduling by default.

RISC-V: Enable pressure-aware scheduling by default.

this patch enables pressure-aware scheduling for riscv.  There have been
various requests for it so I figured I'd just go ahead and send
the patch.

There is some slight regression in code quality for a number of
vector tests where we spill more due to different instructions order.
The ones I looked at were a mix of bad luck and/or brittle tests.
Comparing the size of the generated assembly or the number of vsetvls
for SPECint also didn't show any immediate benefit but that's obviously
not a very fine-grained analysis.

As cost and scheduling models mature I expect the situation to improve
and for now I think it's generally favorable to enable pressure-aware
scheduling so we can work with it rather than trying to find every
possible problem in advance.

gcc/ChangeLog:

	* common/config/riscv/riscv-common.cc: Add -fsched-pressure.
	* config/riscv/riscv.cc (riscv_option_override): Set sched
	pressure algorithm.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/narrow_constraint-1.c: Add
	-fno-sched-pressure.
	* gcc.target/riscv/rvv/base/narrow_constraint-17.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-18.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-19.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-20.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-21.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-22.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-23.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-24.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-25.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-26.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-27.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-28.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-29.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-30.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-31.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-4.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-5.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-8.c: Ditto.
	* gcc.target/riscv/rvv/base/narrow_constraint-9.c: Ditto.
	* gcc.target/riscv/rvv/vsetvl/vlmax_bb_prop-10.c: Ditto.
	* gcc.target/riscv/rvv/vsetvl/vlmax_bb_prop-11.c: Ditto.
	* gcc.target/riscv/rvv/vsetvl/vlmax_bb_prop-12.c: Ditto.
	* gcc.target/riscv/rvv/vsetvl/vlmax_bb_prop-3.c: Ditto.
	* gcc.target/riscv/rvv/vsetvl/vlmax_bb_prop-9.c: Ditto.