cmd/go: disable concurrent compilation under GOEXPERIMENTs

Duplicate cmd/compile check into cmd/go. Manually tested that
"GOEXPERIMENT=fieldtrack make.bash" passes now.

Updates #22223.

Change-Id: I441970a8a5ad4aadf5bd4fbd4d6cc71847b43308
Reviewed-on: https://go-review.googlesource.com/81776
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/internal/work/gc.go

@@ -20,6 +20,7 @@ import (
 	"cmd/go/internal/cfg"
 	"cmd/go/internal/load"
 	"cmd/go/internal/str"
+	"cmd/internal/objabi"
 	"crypto/sha1"
 )
 
@@ -161,6 +162,11 @@ CheckFlags:
 		}
 	}
 
+	// TODO: Test and delete these conditions.
+	if objabi.Fieldtrack_enabled != 0 || objabi.Preemptibleloops_enabled != 0 || objabi.Clobberdead_enabled != 0 {
+		canDashC = false
+	}
+
 	if !canDashC {
 		return 1
 	}