scripts/setlocalversion: factor out 12-chars hash construction

Both of if and else parts append exactly 12 hex chars, but in
different ways.

Factor out the else part because we need to support it without relying
on git-describe. Remove the --abbrev=12 option since we do not use the
hash from git-describe anyway.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Nico Schottelius <nico-linuxsetlocalversion@schottelius.org>

scripts/setlocalversion

@@ -59,24 +59,12 @@ scm_version()
 			fi
 			# If we are past a tagged commit (like
 			# "v2.6.30-rc5-302-g72357d5"), we pretty print it.
-			#
-			# Ensure the abbreviated sha1 has exactly 12
-			# hex characters, to make the output
-			# independent of git version, local
-			# core.abbrev settings and/or total number of
-			# objects in the current repository - passing
-			# --abbrev=12 ensures a minimum of 12, and the
-			# awk substr() then picks the 'g' and first 12
-			# hex chars.
-			if atag="$(git describe --abbrev=12 2>/dev/null)"; then
-				echo "$atag" | awk -F- '{printf("-%05d-%s", $(NF-1),substr($(NF),0,13))}'
-
-			# If we don't have a tag at all we print -g{commitish},
-			# again using exactly 12 hex chars.
-			else
-				head="$(echo $head | cut -c1-12)"
-				printf '%s%s' -g $head
+			if atag="$(git describe 2>/dev/null)"; then
+				echo "$atag" | awk -F- '{printf("-%05d", $(NF-1))}'
 			fi
+
+			# Add -g and exactly 12 hex chars.
+			printf '%s%s' -g "$(echo $head | cut -c1-12)"
 		fi
 
 		# Check for uncommitted changes.