lbmk: use mkhtemp in libreboot's build system

i added a fake -t option, which doesn't actually
read optarg, so that -t usage can just override
the normal template. mkhtemp isn't ready for
distros yet, but it's ready for lbmk.

i hacked the makefile to also copy the binary to
mktemp, and i set PATH in lbmk so that this binary
is used insttead of the one on your system.

that way, upstream projects use it.

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

include/get.sh

@@ -334,7 +334,7 @@ bad_checksum()
 		return 0
 	fi
 
-	build_sbase
+	bootstrap_utils
 	csum="$(x_ "$sha512sum" "$2" | awk '{print $1}')" || \
 	    err "!sha512 '$2' $1" bad_checksum "$@"
 
@@ -355,7 +355,7 @@ tmpclone()
 		return 0
 	fi
 
-	tmpclone_patchlist="`mktemp || err "Can't create tmp patch list"`" || \
+	tmpclone_patchlist="`"$mkhtemp" || err "Can't create tmp patch list"`" || \
 	    err "Can't create tmp patch list" "tmpclone" "$@"
 
 	x_ find "$4" -type f | sort > "$tmpclone_patchlist" || \