bionic: add compatibility mode for properties

Allow a new bionic to work with an old init property area by supporting
the old format.

(cherry picked from commit ad76c85b9ca587084089d086f954158bc0eae905)

Change-Id: Ib496e818a62a5834d40c71eb4745783d998be893
diff --git a/libc/Android.mk b/libc/Android.mk
index b239b74..eba0a00 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -149,6 +149,7 @@
 	bionic/strntoumax.c \
 	bionic/strtotimeval.c \
 	bionic/system_properties.c \
+	bionic/system_properties_compat.c \
 	bionic/tcgetpgrp.c \
 	bionic/tcsetpgrp.c \
 	bionic/thread_atexit.c \