build: Fix non-POSIX commands realpath and mktemp

realpath is not POSIX and not available on all systems.
POSIX mktemp requires a mandatory template argument.

build

@@ -31,7 +31,7 @@ if [[ "$OSTYPE" == "linux-gnu" ]]; then
 	S1INIT=${S1BINS}/stage1_init
 	if [ $GOBIN/init -nt $S1INIT/bin.go ]; then
 		echo "Packaging init (stage1)..."
-		TMP=$(mktemp -d)
+		TMP=$(mktemp -d -t rocket-XXXXXX)
 		[ -d $S1INIT ] || mkdir -p $S1INIT
 		cp $GOBIN/init $TMP/s1init
 		go-bindata -o $S1INIT/bin.go -pkg="stage1_init" -prefix=$TMP $TMP

stage1/mkrootfs.sh

@@ -440,5 +440,5 @@ mkdir "${BINDIR}"
 tar cf "${BINDIR}/s1rootfs.tar" -C "${ROOTDIR}" .
 OUTDIR=$(dirname "${OUTPUT}")
 [ -d "$OUTDIR" ] || mkdir -p "${OUTDIR}"
-go-bindata -o "${OUTPUT}" -prefix $(realpath "${BINDIR}") -pkg=stage1_rootfs "${BINDIR}"
+go-bindata -o "${OUTPUT}" -prefix "${PWD}${BINDIR}" -pkg=stage1_rootfs "${BINDIR}"
 rm -Rf "${WORK}"