build/grub: introduce main(), split it up

easier to read

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

resources/scripts/build/module/grub

@@ -2,7 +2,7 @@
 
 #  helper script: builds GRUB2 source code
 #
-#	Copyright (C) 2014, 2015, 2020 Leah Rowe <info@minifree.org>
+#	Copyright (C) 2014, 2015, 2020, 2023 Leah Rowe <info@minifree.org>
 #   Copyright (C) 2015, 2016 Klemens Nanni <contact@autoboot.org>
 #
 #	This program is free software: you can redistribute it and/or modify
@@ -19,21 +19,20 @@
 #	along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
 
-# This script assumes that the working directory is the root
-# of git or release archive
-
 [ "x${DEBUG+set}" = 'xset' ] && set -v
 set -u -e
 
-# Build GRUB2 as coreboot payload
-
+main()
+{
 	printf "Building GRUB\n"
 
 	if [ ! -d "grub/" ]; then
 		./download grub
 	fi
+}
 
-# use a subshell to not end up in grub/ in case of build issues
+build_grub()
+{
 	(
 	cd grub/
 
@@ -47,3 +46,6 @@ cd grub/
 	./configure --with-platform=coreboot
 	make -j$(nproc)
 	)
+}
+
+main $@