cmd/compile: implement jump table on loong64

cmd/compile: implement jump table on loong64

Following CL 357330, use jump tables on Loong64.

goos: linux
goarch: loong64
pkg: cmd/compile/internal/test
cpu: Loongson-3A6000-HV @ 2500.00MHz
                                 │     old     │                 new                 │
                                 │   sec/op    │   sec/op     vs base                │
Switch8Predictable                 2.352n ± 0%   2.101n ± 0%  -10.65% (p=0.000 n=10)
Switch8Unpredictable               11.99n ± 0%   10.25n ± 0%  -14.51% (p=0.000 n=10)
Switch32Predictable                3.153n ± 0%   1.887n ± 1%  -40.14% (p=0.000 n=10)
Switch32Unpredictable              12.47n ± 0%   10.22n ± 0%  -18.00% (p=0.000 n=10)
SwitchStringPredictable            3.162n ± 0%   3.352n ± 0%   +6.01% (p=0.000 n=10)
SwitchStringUnpredictable          14.70n ± 0%   13.31n ± 0%   -9.46% (p=0.000 n=10)
SwitchTypePredictable              3.702n ± 0%   2.201n ± 0%  -40.55% (p=0.000 n=10)
SwitchTypeUnpredictable            16.18n ± 0%   14.48n ± 0%  -10.51% (p=0.000 n=10)
SwitchInterfaceTypePredictable     7.654n ± 0%   9.680n ± 0%  +26.47% (p=0.000 n=10)
SwitchInterfaceTypeUnpredictable   22.04n ± 0%   22.44n ± 0%   +1.81% (p=0.000 n=10)
geomean                            7.441n        6.469n       -13.07%

Change-Id: Id6f30fa73349c60fac17670084daee56973a955f
Reviewed-on: https://go-review.googlesource.com/c/go/+/705396
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: abner chenc <chenguoqi@loongson.cn>