githooks: skip checksum check for symlink

git will return the target of symlink instead of the content of the file
it points to, which makes the checksum check fail. To fix this we skip
checksum check if object is a symlink.

.githooks/pre-commit

@@ -55,6 +55,11 @@ abuild_local_sources() {
 	return $status
 }
 
+# check if given object is a symlink
+is_symlink() {
+	test "$(git ls-files --stage "$1" | awk '{print $1}')" = "120000"
+}
+
 # Checks that all local sources specified in the APKBUILD file ($1) are
 # available in git tree and checksums are correct.
 check_local_sources() {
@@ -73,6 +78,11 @@ check_local_sources() {
 			status=1
 			continue
 		fi
+
+		if is_symlink ":$startdir/$filename"; then
+			continue
+		fi
+
 		checksum_act=$(git show ":$startdir/$filename" | sha512sum)
 		if [ "$checksum_act" != "$checksum_exp  -" ]; then
 			error "$startdir: bad checksum for file \"$filename\" (hint: run abuild checksum)"