always re-generate .git in lbmk

in release archives, .git is excluded but the version
and versiondate files are included. from these, the
git history is re-created with the exact date (but not
taking into account timezone, at present).

in this way, lbmk will have git history in a release
archive. some build systems, like coreboot, prefer that
there be git history available, so this is a nice
workaround on those build systems.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/err.sh

@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: MIT
 # SPDX-FileCopyrightText: 2022, 2023 Leah Rowe <leah@libreboot.org>
 
-version=""; versiondate=""; projectname=""
+version=""; versiondate=""; projectname=""; _nogit=""
 
 x_() {
 	[ $# -lt 1 ] || ${@} || err_exit err ${@}
@@ -27,6 +27,20 @@ check_git()
 	    git_err "git config --global user.email \"john.doe@example.com\""
 }
 
+# release archives contain .gitignore, but not .git.
+# lbmk can be run from lbmk.git, or an archive.
+git_init()
+{
+	[ -L ".git" ] && ${2} "Reference .git is a symlink"
+	[ -e ".git" ] && return 0
+	eval "$(setvars "$(date -Rd @${versiondate})" cdate _nogit)"
+
+	${1} git init
+	${1} git add -A .
+	${1} git commit -m "${projectname} ${version}" --date "${cdate}"
+	${1} git tag -a "${version}" -m "${projectname} ${version}"
+}
+
 git_err()
 {
 	printf "You need to set git name/email, like so:\n%s\n\n" "${1}" 1>&2