Make a "git describe" fall back for older git versions

--first-parent is not available on CentOS 7.

core/erlc.mk

@@ -309,7 +309,9 @@ endef
 ebin/$(PROJECT).app:: $(ERL_FILES) $(CORE_FILES) $(wildcard src/$(PROJECT).app.src)
 	$(eval FILES_TO_COMPILE := $(filter-out src/$(PROJECT).app.src,$?))
 	$(if $(strip $(FILES_TO_COMPILE)),$(call compile_erl,$(FILES_TO_COMPILE)))
-	$(eval GITDESCRIBE := $(shell git describe --dirty --abbrev=7 --tags --always --first-parent 2>/dev/null || true))
+# Older git versions do not have the --first-parent flag. Do without in that case.
+	$(eval GITDESCRIBE := $(shell git describe --dirty --abbrev=7 --tags --always --first-parent 2>/dev/null \
+		|| git describe --dirty --abbrev=7 --tags --always 2>/dev/null || true))
 	$(eval MODULES := $(patsubst %,'%',$(sort $(notdir $(basename \
 		$(filter-out $(ERLC_EXCLUDE_PATHS),$(ERL_FILES) $(CORE_FILES) $(BEAM_FILES)))))))
 ifeq ($(wildcard src/$(PROJECT).app.src),)