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>

util/libreboot-utils/mkhtemp.c

@@ -68,7 +68,7 @@ main(int argc, char *argv[])
 	xpledgex("stdio flock rpath wpath cpath", NULL);
 
 	while ((c =
-	    getopt(argc, argv, "qdp:")) != -1) {
+	    getopt(argc, argv, "qdp:t")) != -1) {
 
 		switch (c) {
 		case 'd':
@@ -83,6 +83,12 @@ main(int argc, char *argv[])
 			  /* (exit status unchanged) */
 			break;
 
+		case 't':
+			break; /* not supported yet. TODO */
+			/* configured above without optarg,
+			 * so that it is treated as a normal
+			 * template string */
+
 		default:
 			goto err_usage;
 		}