Add explicit dependencies on generated headers.

BUG=None
TEST=emerge-x86-generic, emerge-arm-generic

Change-Id: I9929359ef77793b9756ae2623b4728fb4aa9bd3a
diff --git a/Makefile b/Makefile
index dac90e6..9a21fcf 100644
--- a/Makefile
+++ b/Makefile
@@ -36,6 +36,8 @@
 
 attributes.cc: attributes.pb.h
 
+chaps_adaptor.cc chaps_proxy.cc chaps.cc chapsd.cc: dbus-headers
+
 $(OUT)libchaps.so: dbus-headers \
                    protobufs \
                    $(OUT)chaps.o \