cmd/compile: minor rulegen simplifications
cmd/compile: minor rulegen simplifications

The commuteDepth variable is no longer necessary; remove it.

Else branches after a log.Fatal call are unnecessary.

Also make the unbalanced return an integer, so we can differentiate
positive from negative cases. We only want to continue a rule with the
following lines if this balance is positive, for example.

While at it, make the balance loop stop when it goes negative, to not
let ")(" seem balanced.

Change-Id: I8aa313343ca5a2f07f638b62a0398fdf108fc9eb
Reviewed-on: https://go-review.googlesource.com/c/go/+/228822
Run-TryBot: Daniel Martí <29bf28b42a938ace12a5819da4ed4ba03d82f315@mvdan.cc>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Josh Bleecher Snyder <cdc248cc4d32e4fbfe04e45228163bcecd48a0b9@gmail.com>

akutz/go,CAFxX/go,cloudflare/go,akutz/go,nawawi/go,cloudflare/go,golang/go,nawawi/go,nawawi/go,cloudflare/go,cloudflare/go,CAFxX/go,golang/go,cloudflare/go,cloudflare/go,CAFxX/go,akutz/go,golang/go,CAFxX/go,CAFxX/go,nawawi/go,akutz/go,nawawi/go,nawawi/go,akutz/go,CAFxX/go,nawawi/go,golang/go,akutz/go,golang/go,golang/go,nawawi/go,golang/go,cloudflare/go,akutz/go,akutz/go,golang/go,CAFxX/go,cloudflare/go,CAFxX/go