android: change ANDROID_STL='c++_shared'

- fixes crashes in face-detector application
- libc++_shared.so is bundled automatically via CMake helper project

modules/java/android_sdk/android_gradle_lib/build.gradle

@@ -7,6 +7,13 @@ android {
     defaultConfig {
         minSdkVersion @ANDROID_MIN_SDK_VERSION@
         targetSdkVersion @ANDROID_TARGET_SDK_VERSION@
+
+        externalNativeBuild {
+            cmake {
+                arguments "-DANDROID_STL=@ANDROID_STL@"
+                targets "opencv_jni_shared"
+            }
+        }
     }
 
     buildTypes {
@@ -37,6 +44,12 @@ android {
             manifest.srcFile 'AndroidManifest.xml'
         }
     }
+
+    externalNativeBuild {
+        cmake {
+            path (project.projectDir.toString() + '/libcxx_helper/CMakeLists.txt')
+        }
+    }
 }
 
 dependencies {