Add support to ndk-build in Application.mk

Bug: android/ndk#837
Tests: ./run_tests.py –rebuild –filter weak_symbols_build_support
Change-Id: I08b45b667a7480fc6e68d6edffeecdb14700cde0

build/core/default-build-commands.mk

@@ -119,6 +119,11 @@ GLOBAL_CFLAGS += \
 
 GLOBAL_CFLAGS += -D_FORTIFY_SOURCE=2
 
+
+ifeq ($(APP_WEAK_API_DEFS), true)
+  GLOBAL_CFLAGS += -D__ANDROID_UNAVAILABLE_SYMBOLS_ARE_WEAK__
+endif
+
 GLOBAL_LDFLAGS = \
     -target $(LLVM_TRIPLE)$(TARGET_PLATFORM_LEVEL) \
     -no-canonical-prefixes \

build/core/definitions.mk

@@ -1192,6 +1192,7 @@ NDK_APP_VARS_OPTIONAL := \
     APP_STL \
     APP_STRIP_MODE \
     APP_THIN_ARCHIVE \
+    APP_WEAK_API_DEFS \
     APP_WRAP_SH \
 
 # NDK_ALL_ABIS is not configured yet.

tests/device/weak_symbols_build_support/jni/Android.mk

@@ -0,0 +1,10 @@
+LOCAL_PATH := $(call my-dir)
+
+include $(CLEAR_VARS)
+LOCAL_MODULE := weak_symbols
+LOCAL_SRC_FILES := weak_symbols.cpp
+LOCAL_STATIC_LIBRARIES := googletest_main
+LOCAL_LDLIBS := -landroid
+include $(BUILD_EXECUTABLE)
+
+$(call import-module,third_party/googletest)

tests/device/weak_symbols_build_support/jni/Application.mk

@@ -0,0 +1,2 @@
+APP_STL := c++_static
+APP_WEAK_API_DEFS := true

tests/device/weak_symbols_build_support/jni/weak_symbols.cpp

@@ -0,0 +1,14 @@
+#include <gtest/gtest.h>
+#include <android/trace.h>
+#include <android/api-level.h>
+
+TEST(weak_symbols, weak_symbol_enable) {
+     bool called = false;
+     if (__builtin_available(android 29, *)) {
+       // 0 is an arbitrary cookie. The specific value doesn't matter because
+       // this will never run concurrently.
+       ATrace_beginAsyncSection("ndk::asyncBeginEndSection", 0);
+       called = true;
+     }
+     ASSERT_EQ(android_get_device_api_level() >= 29, called);
+}