run-as: Use Minijail for privilege dropping.

Arguably, we don't need a ScopedMinijail for a program that only execs,
but I'd rather keep the code consistent and have all uses of Minijail
be good examples.

Bug: 30156807

Change-Id: I08a968835e0f3e2afcd5e7736626edbed658cde2
diff --git a/run-as/Android.mk b/run-as/Android.mk
index 2e305d7..7111fbe 100644
--- a/run-as/Android.mk
+++ b/run-as/Android.mk
@@ -1,8 +1,8 @@
 LOCAL_PATH:= $(call my-dir)
 
 include $(CLEAR_VARS)
-LOCAL_CFLAGS := -Werror
+LOCAL_CFLAGS := -Wall -Werror
 LOCAL_MODULE := run-as
-LOCAL_SHARED_LIBRARIES := libselinux libpackagelistparser
+LOCAL_SHARED_LIBRARIES := libselinux libpackagelistparser libminijail
 LOCAL_SRC_FILES := run-as.cpp
 include $(BUILD_EXECUTABLE)