Add debug build support for Android native code (#25147)

Summary:
With JSI based architecture, there will be more and more C++ native code involved.
Original NDK builder in RN only supports release build and that's not reasonable for native debugging.
This change introduces a way to build native code in debuggable version.

Simply add `NATIVE_BUILD_TYPE=Debug` environment variable during gradle build,
e.g.
`NATIVE_BUILD_TYPE=Debug ./gradlew clean :ReactAndroid:assembleDebug`

## Changelog

[Android] [Added] - Add native debug build support to improve debugging DX
Pull Request resolved: https://github.com/facebook/react-native/pull/25147

Differential Revision: D15628533

Pulled By: cpojer

fbshipit-source-id: 8f5b54c4580824452d2a1236a7bd641889b001ec

ReactAndroid/src/main/jni/react/jni/Android.mk

@@ -36,6 +36,14 @@ LOCAL_MODULE := reactnativejni
 # Compile all local c++ files.
 LOCAL_SRC_FILES := $(wildcard *.cpp)
 
+ifeq ($(APP_OPTIM),debug)
+  # Keep symbols by overriding the strip command invoked by ndk-build.
+  # Note that this will apply to all shared libraries,
+  # i.e. shared libraries will NOT be stripped
+  # even though we override it in this Android.mk
+  cmd-strip :=
+endif
+
 # Build the files in this directory as a shared library
 include $(BUILD_SHARED_LIBRARY)
 

ReactAndroid/src/main/jni/third-party/folly/Android.mk

@@ -17,6 +17,14 @@ LOCAL_SRC_FILES:= \
   folly/container/detail/F14Table.cpp \
   folly/ScopeGuard.cpp \
 
+ifeq ($(APP_OPTIM),debug)
+  LOCAL_SRC_FILES += \
+    folly/lang/Assume.cpp \
+    folly/lang/SafeAssert.cpp \
+    folly/FileUtil.cpp \
+    folly/portability/SysUio.cpp
+endif
+
 LOCAL_C_INCLUDES := $(LOCAL_PATH)
 LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)