Platform: disable hidden visibility for Android Native App Glue.

Otherwise the ANativeActivity_onCreate() won't get exported and the
app will fail to start. Of course they just don't care and produce
crappy code that apparently nobody uses in production environment.

src/Magnum/Platform/CMakeLists.txt

@@ -75,6 +75,10 @@ if(WITH_ANDROIDAPPLICATION)
         ${MagnumAndroidApplication_HEADERS}
         ${MagnumAndroidApplication_PRIVATE_HEADERS}
         ${ANDROID_NATIVE_APP_GLUE_SRC})
+    # They just don't care, so of course the ANativeActivity_onCreate()
+    # function is not exported and thus the app startup fails if I don't
+    # disable hidden visibility for the file.
+    set_source_files_properties(${ANDROID_NATIVE_APP_GLUE_SRC} PROPERTIES COMPILE_FLAGS "-fvisibility=default")
     target_include_directories(MagnumAndroidApplication PUBLIC ${ANDROID_NATIVE_APP_GLUE_INCLUDE_DIR})
     set_target_properties(MagnumAndroidApplication PROPERTIES DEBUG_POSTFIX "-d")
     # Assuming that PIC is not needed because the Application lib is always