add a compiler flag to use script.c instead of script-stub.c

this change is needed for Android Virtual Device (AVD) on
GCE (Google Compute Engine).

Bug: 27336968
Change-Id: I838683a1ca6558d4226aa5b3b0d2996d0ecfaa72
diff --git a/Android.mk b/Android.mk
index 4ae22f6..8a5a9b2 100644
--- a/Android.mk
+++ b/Android.mk
@@ -35,7 +35,6 @@
     dhcp.c \
     ipv4.c \
     ipv4ll.c \
-    script-stub.c \
     ifaddrs.c \
     crypt/md5.c \
     crypt/hmac_md5.c \
@@ -47,6 +46,12 @@
 # Always support IPv4.
 LOCAL_CFLAGS += -DINET
 
+ifeq ($(DHCPCD_USE_SCRIPT), yes)
+LOCAL_SRC_FILES += script.c
+else
+LOCAL_SRC_FILES += script-stub.c
+endif
+
 ifeq ($(DHCPCD_USE_IPV6), yes)
 LOCAL_SRC_FILES += ipv6.c ipv6nd.c dhcp6.c
 LOCAL_SRC_FILES += crypt/sha256.c