cmd/compile/internal/gc: remove stringsCompare

Inlined the last occurrence of stringsCompare into exprcmp.

Passes go build -a -toolexec 'toolstash -cmp' std cmd.

Change-Id: I8fd99e3fbffc84283cc269368595cba950533066
Reviewed-on: https://go-review.googlesource.com/14872
Reviewed-by: Dave Cheney <dave@cheney.net>
Run-TryBot: Dave Cheney <dave@cheney.net>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/cmd/compile/internal/gc/swt.go b/src/cmd/compile/internal/gc/swt.go
index f5952fc..9ed30b2 100644
--- a/src/cmd/compile/internal/gc/swt.go
+++ b/src/cmd/compile/internal/gc/swt.go
@@ -778,7 +778,13 @@
 		if len(a) > len(b) {
 			return +1
 		}
-		return stringsCompare(a, b)
+		if a == b {
+			return 0
+		}
+		if a < b {
+			return -1
+		}
+		return +1
 	}
 
 	return 0