cmd/compile: indicate sense of hash/bisect match in output

If a hash match is "disabled" (!enabled) indicate that in the
output with DISABLED.  This is helpful in ensuring that multiple
package-directed command-line flags have the intended behavior,
e.g.

```
go build -a                       \
-gcflags=all=-d=gossahash=vn      \
-gcflags=runtime=-d=gossahash=vy  \
std
```

Output looks like

[DISABLED] [bisect-match 0x11d0ee166d9d61b4]

or (w/ "v"-prefixed hashcode )

sort/slice.go:23:29 note [DISABLED] [bisect-match 0xa5252e1c1b85f2ec]
gossahash triggered sort/slice.go:23:29 note [DISABLED] 100001011111001011101100

Change-Id: I797e02b3132f9781d97bacd0dcd2e80af0035cd8
Reviewed-on: https://go-review.googlesource.com/c/go/+/497216
Reviewed-by: Russ Cox <[email protected]>
Run-TryBot: David Chase <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: dr2chase

src/cmd/compile/internal/base/hashdebug.go

@@ -286,19 +286,25 @@ func (d *HashDebug) matchPos(ctxt *obj.Link, pos src.XPos, note func() string) b
 // change is selected.
 func (d *HashDebug) matchAndLog(hash uint64, text, note func() string) bool {
 	if d.bisect != nil {
+		enabled := d.bisect.ShouldEnable(hash)
 		if d.bisect.ShouldPrint(hash) {
+			disabled := ""
+			if !enabled {
+				disabled = " [DISABLED]"
+			}
 			var t string
 			if !d.bisect.MarkerOnly() {
 				t = text()
 				if note != nil {
 					if n := note(); n != "" {
-						t += ": " + n
+						t += ": " + n + disabled
+						disabled = ""
 					}
 				}
 			}
-			d.log(d.name, hash, t)
+			d.log(d.name, hash, strings.TrimSpace(t+disabled))
 		}
-		return d.bisect.ShouldEnable(hash)
+		return enabled
 	}
 
 	// TODO: Delete rest of function body when we switch to bisect-only.

src/cmd/compile/internal/base/hashdebug_test.go

@@ -93,8 +93,8 @@ func TestNMatch(t *testing.T) {
 	if check {
 		t.Errorf("GOSSAHASH=n should NOT have matched for 'bar', '0'")
 	}
-	wantPrefix(t, msg, "bar.0 [bisect-match ")
-	wantContains(t, msg, "\nGOSSAHASH triggered bar.0 010100100011100101011110")
+	wantPrefix(t, msg, "bar.0 [DISABLED] [bisect-match ")
+	wantContains(t, msg, "\nGOSSAHASH triggered bar.0 [DISABLED] 010100100011100101011110")
 }
 
 func TestHashNoMatch(t *testing.T) {