Update Makefile VERSION assignment to avoid errors when not in a git …

…repository

Simplify the VERSION assignment to prevent the "fatal: not a git repository (or any of the parent directories): .git" error when building from a source archive. The VERSION variable now checks if the Makefile is within a git working tree before attempting to use git tags. If not, it defaults to "v0.7", avoiding errors in non-git environments.

Makefile

@@ -1,5 +1,5 @@
 # "Makefile" for graftcp.
-# Copyright (C) 2016, 2018, 2020, 2021, 2023 Hmgle <[email protected]>
+# Copyright (C) 2016, 2018, 2020, 2021, 2023, 2024 Hmgle <[email protected]>
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -19,7 +19,8 @@ ifneq ($(KERNEL), Linux)
 $(error only support Linux now.)
 endif
 
-VERSION = $(shell git describe --tags --always)
+VERSION = $(shell git rev-parse --is-inside-work-tree 1>/dev/null 2>&1 && \
+             git describe --tags --always || echo "v0.7")
 
 # CROSS_COMPILE can be set on the command line
 # make CROSS_COMPILE=arm-linux-gnueabi-
@@ -45,9 +46,6 @@ else
 	CFLAGS += -O2 -DNDEBUG
 endif
 
-ifneq ($(shell echo $(VERSION) | head -c 1), v)
-	VERSION=v0.7
-endif
 CFLAGS += -DVERSION=\"$(VERSION)\"
 
 SRC := $(wildcard *.c)