cmd/compile: add specialized AddArgN functions for rewrite rules

This shrinks the compiler without impacting performance.
(The performance-sensitive part of rewrite rules is the non-match case.)
Passes toolstash-check -all.

Executable size:

file    before    after     Δ       %       
compile 20356168  20163960  -192208 -0.944% 
total   115599376 115407168 -192208 -0.166% 

Text size:

file                       before   after    Δ       %       
cmd/compile/internal/ssa.s 3928309  3778774  -149535 -3.807% 
total                      18862943 18713408 -149535 -0.793% 

Memory allocated compiling package SSA:

SSA               12.7M ± 0%        12.5M ± 0%  -1.74%  (p=0.008 n=5+5)

Compiler speed impact:

name        old time/op       new time/op       delta
Template          211ms ± 1%        211ms ± 2%    ~     (p=0.832 n=49+49)
Unicode          82.8ms ± 2%       83.2ms ± 2%  +0.44%  (p=0.022 n=46+49)
GoTypes           726ms ± 1%        728ms ± 2%    ~     (p=0.076 n=46+48)
Compiler          3.39s ± 2%        3.40s ± 2%    ~     (p=0.633 n=48+49)
SSA               7.71s ± 1%        7.65s ± 1%  -0.78%  (p=0.000 n=45+44)
Flate             134ms ± 1%        134ms ± 1%    ~     (p=0.195 n=50+49)
GoParser          167ms ± 1%        167ms ± 1%    ~     (p=0.390 n=47+47)
Reflect           453ms ± 3%        452ms ± 2%    ~     (p=0.492 n=48+49)
Tar               184ms ± 3%        184ms ± 2%    ~     (p=0.862 n=50+48)
XML               248ms ± 2%        248ms ± 2%    ~     (p=0.096 n=49+47)
[Geo mean]        415ms             415ms       -0.03%

name        old user-time/op  new user-time/op  delta
Template          273ms ± 1%        273ms ± 2%    ~     (p=0.711 n=48+48)
Unicode           117ms ± 6%        117ms ± 5%    ~     (p=0.633 n=50+50)
GoTypes           972ms ± 2%        974ms ± 1%  +0.29%  (p=0.016 n=47+49)
Compiler          4.46s ± 6%        4.51s ± 6%    ~     (p=0.093 n=50+50)
SSA               10.4s ± 1%        10.3s ± 2%  -0.94%  (p=0.000 n=45+50)
Flate             166ms ± 2%        167ms ± 2%    ~     (p=0.148 n=49+48)
GoParser          202ms ± 1%        202ms ± 2%  -0.28%  (p=0.014 n=47+49)
Reflect           594ms ± 2%        594ms ± 2%    ~     (p=0.717 n=48+49)
Tar               224ms ± 2%        224ms ± 2%    ~     (p=0.805 n=50+49)
XML               311ms ± 1%        310ms ± 1%    ~     (p=0.177 n=49+48)
[Geo mean]        537ms             537ms       +0.01%


Change-Id: I562b9f349b34ddcff01771769e6dbbc80604da7a
Reviewed-on: https://go-review.googlesource.com/c/go/+/221237


Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>