Fix folly::dynamic crash when attaching a debugger to Hermes

Summary:
folly_futures was compiled with and exported -DFOLLY_MOBILE=1, while
folly_json did not. This flag disables fancy F14 data structures for
folly::dynamic in favor of a simple std::unordered_map.

This caused inlined/templated code from modules depending on
folly_futures to disagree with the implementations in folly_json,
leading to a crash.

The only such libraries were libhermes-inspector and (transitively)
libhermes-executor-debug, and these only use folly::dynamic for CDP
serialization, which is why the problem was not more apparent.

Changelog: [Internal] Fix crash when attaching a Hermes debugger

Reviewed By: mhorowitz

Differential Revision: D21193307

fbshipit-source-id: 2b795bb6f4f7f991e2adaacec62d62616117322b

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

@@ -36,7 +36,8 @@ FOLLY_FLAGS := \
   -DFOLLY_NO_CONFIG=1 \
   -DFOLLY_HAVE_CLOCK_GETTIME=1 \
   -DFOLLY_HAVE_MEMRCHR=1 \
-  -DFOLLY_USE_LIBCPP=1
+  -DFOLLY_USE_LIBCPP=1 \
+  -DFOLLY_MOBILE=1
 
 # If APP_PLATFORM in Application.mk targets android-23 above, please comment this line.
 # NDK uses GNU style stderror_r() after API 23.
@@ -87,9 +88,6 @@ LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)
 
 LOCAL_CFLAGS += -fexceptions -fno-omit-frame-pointer -frtti -Wno-sign-compare
 
-FOLLY_FLAGS += \
-  -DFOLLY_MOBILE=1
-
 LOCAL_CFLAGS += $(FOLLY_FLAGS)
 
 LOCAL_EXPORT_CPPFLAGS := $(FOLLY_FLAGS)