config/git: import suckless sbase

i currently use the output of sha512sum in several
places of xbmk, which is a bit unreliable in case
output changes.

other cases where i use util outputs in variables
are probably reliable, because i'm using mostly
posix utilities in those.

to mitigate this, i now import suckless sbase, which
has a reasonable sha512sum implementation.

*every* binary it builds is being placed in build.list,
because i'll probably start using more of them.

for example, i may start modifying the "date"
implementation, adding the GNU-specific options that
i need as mentioned on init.sh

i'm importing it in util/ because the sha512sum
util is needed for verifying project sources, so
if sbase itself is a "project source", that means
we can into a chicken and egg bootstrapping problem.

this is sbase at revision:
055cc1ae1b3a13c3d8f25af0a4a3316590efcd48

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

util/sbase/chroot.c

@@ -0,0 +1,49 @@
+/* See LICENSE file for copyright and license details. */
+#include <errno.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "util.h"
+
+static void
+usage(void)
+{
+	eprintf("usage: %s dir [cmd [arg ...]]\n", argv0);
+}
+
+int
+main(int argc, char *argv[])
+{
+	char *shell[] = { "/bin/sh", "-i", NULL }, *aux, *cmd;
+	int savederrno;
+
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND
+
+	if (!argc)
+		usage();
+
+	if ((aux = getenv("SHELL")))
+		shell[0] = aux;
+
+	if (chroot(argv[0]) < 0)
+		eprintf("chroot %s:", argv[0]);
+
+	if (chdir("/") < 0)
+		eprintf("chdir:");
+
+	if (argc == 1) {
+		cmd = *shell;
+		execvp(cmd, shell);
+	} else {
+		cmd = argv[1];
+		execvp(cmd, argv + 1);
+	}
+
+	savederrno = errno;
+	weprintf("execvp %s:", cmd);
+
+	_exit(126 + (savederrno == ENOENT));
+}