servo: Merge #2899 - Fix submodule dependencies for string cache (from glennw:fix-deps)

Source-Repo: https://github.com/servo/servo
Source-Revision: 3c35a83939c4814d957f16f697e23b6fd0b1d1fe

servo/mk/sub.mk

@@ -100,6 +100,11 @@ DEPS_rust-http += \
 	rust-url \
 	$(NULL)
 
+DEPS_string-cache += \
+	rust-phf \
+	rust \
+	$(NULL)
+
 # Platform-specific dependencies
 ifeq ($(CFG_OSTYPE),apple-darwin)
 DEPS_rust-azure += \