Include Flatbuffers as source when building for mobile

The mobile platforms do not include the dependencies as part of the package step, so what the previous build system did was just include flatbuffers source files directly in app, which will be duplicated here.

Author: a-maurice

app/CMakeLists.txt

@@ -298,6 +298,15 @@ else()
       "${app_desktop_HDRS}")
 endif()
 
+if(ANDROID OR IOS)
+  # If building for Android or iOS, include the Flatbuffers source files directly.
+  set(app_flatbuffers_srcs ${FlatBuffers_Library_SRCS})
+  set(app_flatbuffers_lib)
+else()
+  set(app_flatbuffers_srcs)
+  set(app_flatbuffers_lib flatbuffers)
+endif()
+
 add_library(firebase_app STATIC
     ${log_SRCS}
     ${log_HDRS}
@@ -311,7 +320,8 @@ add_library(firebase_app STATIC
     memory/atomic.h
     meta/move.h
     memory/unique_ptr.h
-    memory/shared_ptr.h)
+    memory/shared_ptr.h
+    ${app_flatbuffers_srcs})
 
 set_property(TARGET firebase_app PROPERTY FOLDER "Firebase Cpp")
 
@@ -339,7 +349,7 @@ target_compile_definitions(firebase_app
 # firebase_app has a dependency on flatbuffers, which needs to be included.
 target_link_libraries(firebase_app
   PRIVATE
-    flatbuffers
+    ${app_flatbuffers_lib}
     ${LIBSECRET_LIBRARIES}
 )
 # Automatically include headers that might not be declared.
@@ -533,4 +543,4 @@ if (IOS)
   # to destination dir "Headers/google_play_services/*"
   set_property(SOURCE "src/include/google_play_services/availability.h" PROPERTY 
                   MACOSX_PACKAGE_LOCATION Headers/google_play_services)
-endif()
+endif()