Android: Allow NDK location to be overridden

Source/Android/app/build.gradle

@@ -161,6 +161,14 @@ String getGitPath() {
 }
 
 String getNdkPath() {
+    def propsFile = rootProject.file("build.properties")
+    def ndkPath = null
+    if (propsFile.canRead()) {
+        def buildProperties = new Properties()
+        buildProperties.load(new FileInputStream(propsFile))
+        ndkPath = buildProperties.ndkPath
+    }
+    if (ndkPath == null) {
         try {
             def stdout = new ByteArrayOutputStream()
 
@@ -171,15 +179,15 @@ String getNdkPath() {
             }
 
             def ndkCmdPath = stdout.toString()
-        def ndkPath = ndkCmdPath.substring(0, ndkCmdPath.lastIndexOf('/'))
-
-        project.logger.quiet("Gradle: Found Android NDK:" + ndkPath)
-
-        return ndkPath
+            ndkPath = ndkCmdPath.substring(0, ndkCmdPath.lastIndexOf('/'))
         } catch (ignored) {
             project.logger.error("Gradle error: Couldn't find NDK.")
-        return null;
         }
+    }
+    if (ndkPath != null) {
+        project.logger.quiet("Gradle: Found Android NDK: " + ndkPath)
+    }
+    return ndkPath
 }
 
 String getAbi() {