Add dependencies for files in LOCAL_PROGUARD_FLAGS

Do this by introducing a new LOCAL_PROGUARD_FLAGS_DEPS variable that we
can modify anytime we add a file reference to LOCAL_PROGUARD_FLAGS.

An alternative would have been to switch to LOCAL_PROGUARD_FLAG_FILES,
but that would have been much harder to ensure the same command line
ordering.

Bug: 130111713
Test: treehugger
Change-Id: If367197b30d563e0796f0cafa00be1f275f2c406
diff --git a/core/static_java_library.mk b/core/static_java_library.mk
index cb3281a..7eef167 100644
--- a/core/static_java_library.mk
+++ b/core/static_java_library.mk
@@ -74,6 +74,7 @@
 endif
 
 LOCAL_PROGUARD_FLAGS := $(addprefix -include ,$(proguard_options_file)) $(LOCAL_PROGUARD_FLAGS)
+LOCAL_PROGUARD_FLAGS_DEPS += $(proguard_options_file)
 
 R_file_stamp := $(intermediates.COMMON)/src/R.stamp
 LOCAL_INTERMEDIATE_TARGETS += $(R_file_stamp)