-NOTMUCH_DEPENDS_FLAGS=-I./lib `pkg-config --cflags glib-2.0 gmime-2.4 talloc`
-NOTMUCH_CXX_DEPENDS_FLAGS=$(NOTMUCH_DEPENDS_FLAGS) `xapian-config --cxxflags`
+# Additional flags that we will append to whatever the user set.
+# These aren't intended for the user to manipulate.
+extra_cflags = `pkg-config --cflags glib-2.0 gmime-2.4 talloc`
+extra_cxxflags = `xapian-config --cxxflags`