Support to add JNI of both archs in multilib build.

Use "LOCAL_MULTILIB := both" to install jni libraries of both archs in
multilib build.
The build system will package jni of both archs to the apk, or install
them to the right location on the system image and create symlinks,
extract .so files from prebuilt apk, etc if appropriate.

Bug: 15849902
Change-Id: I7e147b5a47db476584c38250de7b36c75ea40d81
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index c6a09d8..84aaa57 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -167,6 +167,7 @@
 LOCAL_GENERATED_SOURCES_$(TARGET_ARCH):=
 LOCAL_REQUIRED_MODULES_$(TARGET_ARCH):=
 LOCAL_CLANG_$(TARGET_ARCH):=
+LOCAL_PREBUILT_JNI_LIBS_$(TARGET_ARCH):=
 ifdef TARGET_2ND_ARCH
 LOCAL_SRC_FILES_$(TARGET_2ND_ARCH):=
 LOCAL_CFLAGS_$(TARGET_2ND_ARCH):=
@@ -181,6 +182,7 @@
 LOCAL_GENERATED_SOURCES_$(TARGET_2ND_ARCH):=
 LOCAL_REQUIRED_MODULES_$(TARGET_2ND_ARCH):=
 LOCAL_CLANG_$(TARGET_2ND_ARCH):=
+LOCAL_PREBUILT_JNI_LIBS_$(TARGET_2ND_ARCH):=
 endif
 LOCAL_SRC_FILES_$(HOST_ARCH):=
 LOCAL_CFLAGS_$(HOST_ARCH):=