Create symlink for 'usr/include' in the staging directory so that packages like zlib and others who expect that to exist will install properly.

Makefile

@@ -107,6 +107,7 @@ $(STAGING_DIR):
 	@mkdir -p $(STAGING_DIR)/include
 	@mkdir -p $(STAGING_DIR)/usr
 	@mkdir -p $(STAGING_DIR)/$(REAL_GNU_TARGET_NAME)
+	@ln -snf ../include $(STAGING_DIR)/usr/include
 	@ln -snf ../lib $(STAGING_DIR)/usr/lib
 	@ln -snf ../lib $(STAGING_DIR)/$(REAL_GNU_TARGET_NAME)/lib