Fix the undefined CommandDeps for standard Javadoc

When compiling against without customized doclet, Javadoc doesn't need
to depend on Doclava and Jsilver jars. Originally, we leave these two
jars empty in Args so that CommandDeps won't have these two
dependencies. But Ninja doesn't like that with errors:

ninja: error: build.ninja: empty path
because $Jsilver and $Doclava is undefined when compiling Javadoc.

Test: m -j platform_library-docs
Bug: b/70351683
Change-Id: I02fee181490f91e87a1feac74f3a69b5b4acb528
diff --git a/java/droiddoc.go b/java/droiddoc.go
index a29f0ba..4dd5fbb 100644
--- a/java/droiddoc.go
+++ b/java/droiddoc.go
@@ -38,15 +38,13 @@
 				"${config.ZipSyncCmd}",
 				"${config.JavadocCmd}",
 				"${config.SoongZipCmd}",
-				"$JsilverJar",
-				"$DoclavaJar",
 			},
 			Rspfile:        "$out.rsp",
 			RspfileContent: "$in",
 			Restat:         true,
 		},
 		"outDir", "srcJarDir", "stubsDir", "srcJars", "opts",
-		"bootclasspathArgs", "classpathArgs", "sourcepath", "docZip", "JsilverJar", "DoclavaJar")
+		"bootclasspathArgs", "classpathArgs", "sourcepath", "docZip")
 )
 
 func init() {
@@ -577,8 +575,13 @@
 
 	implicits = append(implicits, d.Javadoc.srcJars...)
 
+	jsilver := android.PathForOutput(ctx, "host", ctx.Config().PrebuiltOS(), "framework", "jsilver.jar")
+	doclava := android.PathForOutput(ctx, "host", ctx.Config().PrebuiltOS(), "framework", "doclava.jar")
+	implicits = append(implicits, jsilver)
+	implicits = append(implicits, doclava)
+
 	opts := "-source 1.8 -J-Xmx1600m -J-XX:-OmitStackTraceInFastThrow -XDignore.symbol.file " +
-		"-doclet com.google.doclava.Doclava -docletpath ${config.JsilverJar}:${config.DoclavaJar} " +
+		"-doclet com.google.doclava.Doclava -docletpath " + jsilver.String() + ":" + doclava.String() + " " +
 		"-templatedir " + templateDir + " " + htmlDirArgs + " " + htmlDir2Args + " " +
 		"-hdf page.build " + ctx.Config().BuildId() + "-" + ctx.Config().BuildNumberFromFile() + " " +
 		"-hdf page.now " + `"$$(date -d @$$(cat ` + ctx.Config().Getenv("BUILD_DATETIME_FILE") + `) "+%d %b %Y %k:%M")"` +
@@ -609,8 +612,6 @@
 			"classpathArgs":     classpathArgs,
 			"sourcepath":        strings.Join(d.Javadoc.sourcepaths.Strings(), ":"),
 			"docZip":            d.Javadoc.docZip.String(),
-			"JsilverJar":        "${config.JsilverJar}",
-			"DoclavaJar":        "${config.DoclavaJar}",
 		},
 	})
 }