Makefile: Add multiple methods of determining the version number

This fixes m1n1 stage2 version numbers (for .tar.gz downloads) as long
as the directory name is left intact, and also supports packagers
passing their own version number if needed.

Signed-off-by: Hector Martin <[email protected]>

Author: marcan

Makefile

@@ -203,7 +203,7 @@ build/$(NAME).bin: build/$(NAME)-raw.elf
 
 update_tag:
 	@mkdir -p build
-	@echo "#define BUILD_TAG \"$$(git describe --tags --always --dirty)\"" > build/build_tag.tmp
+	@./version.sh > build/build_tag.tmp
 	@cmp -s build/build_tag.h build/build_tag.tmp 2>/dev/null || \
 	( mv -f build/build_tag.tmp build/build_tag.h && echo "  TAG   build/build_tag.h" )
 

version.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+cd "$(dirname "$0")"
+
+dirbase="$(basename "$(pwd)")"
+
+if [ -n "$M1N1_VERSION_TAG" ]; then
+    version="$M1N1_VERSION_TAG"
+elif [ -e ".git" ]; then
+    version="$(git describe --tags --always --dirty)"
+elif [ "${dirbase:0:5}" == "m1n1-" ]; then
+    version="${dirbase:5}"
+    version="v${version##v}"
+else
+    version="unknown"
+fi
+
+echo "#define BUILD_TAG \"$version\""