Rewrite depfile from sbox to stay reproducible

sbox will generate a random directory for the output root, and most
tools will encode that directory name in the output target of the
depfile.

So embed the library from dep_fixer into sbox so that it can rewrite the
output filename to a static (reproducible) value. Ninja doesn't care
what that value is, so it's just "outputfile".

Also fix up rule_builder to actually tell sbox about the depfile.

Test: mmma system/iorap; check the contents of:
out/soong/.intermediates/system/iorap/libiorap-binder/android_arm_armv7-a-neon_core_static/gen/aidl/system/iorap/binder/com/google/android/startop/iorap/IIorap.cpp.d

Change-Id: I3640a2e8b0c034f143a35e398a8418a6d621b265
diff --git a/android/rule_builder.go b/android/rule_builder.go
index 48d070e..6f04672 100644
--- a/android/rule_builder.go
+++ b/android/rule_builder.go
@@ -367,10 +367,6 @@
 			sboxOutputs[i] = "__SBOX_OUT_DIR__/" + Rel(ctx, r.sboxOutDir.String(), output.String())
 		}
 
-		if depFile != nil {
-			sboxOutputs = append(sboxOutputs, "__SBOX_OUT_DIR__/"+Rel(ctx, r.sboxOutDir.String(), depFile.String()))
-		}
-
 		commandString = proptools.ShellEscape(commandString)
 		if !strings.HasPrefix(commandString, `'`) {
 			commandString = `'` + commandString + `'`
@@ -380,8 +376,13 @@
 		sboxCmd.BuiltTool(ctx, "sbox").
 			Flag("-c").Text(commandString).
 			Flag("--sandbox-path").Text(shared.TempDirForOutDir(PathForOutput(ctx).String())).
-			Flag("--output-root").Text(r.sboxOutDir.String()).
-			Flags(sboxOutputs)
+			Flag("--output-root").Text(r.sboxOutDir.String())
+
+		if depFile != nil {
+			sboxCmd.Flag("--depfile-out").Text(depFile.String())
+		}
+
+		sboxCmd.Flags(sboxOutputs)
 
 		commandString = sboxCmd.buf.String()
 		tools = append(tools, sboxCmd.tools...)