util/lint: Update tools that use git to use a library

Each of the tools that used git had similar functionality. This combines
all of that into a single script that gets sourced by each.  This makes
maintenance much easier.

By doing this and updating each of the scripts to do the correct thing
if the script isn't being run in a git repository, it makes them work
much better for the releases, which are just released as a tarball,
without any attached git repository.

Change-Id: I61ba1cc4f7205e0d4baf993588bbc774120405cb
Signed-off-by: Martin Roth <martin@coreboot.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/64973
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>

util/lint/lint-stable-018-symlinks

@@ -4,21 +4,23 @@
 
 # DESCR: Report any symbolic links
 
-LC_ALL=C export LC_ALL
+LINTDIR="$(
+  cd -- "$(dirname "$0")" > /dev/null 2>&1 || return
+  pwd -P
+)"
+
+# shellcheck source=helper_functions.sh
+. "${LINTDIR}/helper_functions.sh"
 
 EXCLUDED_DIRS='^3rdparty\|^site-local'
 
-# If the code is in a git repo, only print files that are checked in
-if [ -n "$(command -v git)" ] && \
-	[ "$(git rev-parse --is-inside-work-tree 2>/dev/null)" = "true" ]
-then
-	git ls-tree -r HEAD | \
-		grep ^120000 | \
-		cut -f2 | \
-		grep -v "$EXCLUDED_DIRS"
-else
-	# If the code isn't in a git repo, print everything
-	find . -type l | \
-		sed 's|\.\/||' | \
-		grep -v "$EXCLUDED_DIRS"
+# Exit if the code isn't in a git repo
+if [ "${IN_GIT_TREE}" -eq 0 ]; then
+	exit 0
 fi
+
+
+${GIT} ls-tree -r HEAD | \
+	grep ^120000 | \
+	cut -f2 | \
+	grep -v "$EXCLUDED_DIRS"