A try to get build directory name from gradle.

app/build.gradle

@@ -36,7 +36,8 @@ preBuild.dependsOn createVersionXML
 //
 task generateDrawablesFromArt {
 	doLast {
-        def p = 'make -C app/src/main/art RES=../res TMP=../../../build/art'.execute()
+		def buildDir = (new File(project.buildDir,'art')).toString()
+        def p = ('make -C app/src/main/art RES=../res TMP='+buildDir).execute()
 		p.consumeProcessOutput()
 		p.waitFor()
 		if ( p.exitValue() )