[dev.typeparams] internal/buildcfg: allow regabiwrappers on all GOARCH

There's nothing GOARCH-specific about ABI wrappers, so allow enabling
them on all architectures.

For unified IR, I want to have a testing mode where we add dictionary
parameters even to non-generic functions, as a way to help stress test
that they're handled correctly. This requires callers to know to
supply the appropriate dictionary arguments when calling them. Calls
generated by the Go compiler know to do this, but calls written in
assembly won't.

Reusing the regabi wrappers is a convenient choke-point for inserting
dictionary arguments for assembly calls.

Change-Id: Ic2c06b7626730289c5405829b61653d1daec430b
Reviewed-on: https://go-review.googlesource.com/c/go/+/333453
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

src/internal/buildcfg/exp.go

@@ -111,7 +111,6 @@ func ParseGOEXPERIMENT(goos, goarch, goexp string) (flags, baseline goexperiment
 	}
 	// regabi is only supported on amd64 and arm64.
 	if goarch != "amd64" && goarch != "arm64" {
-		flags.RegabiWrappers = false
 		flags.RegabiReflect = false
 		flags.RegabiArgs = false
 	}