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/env.c

@@ -0,0 +1,49 @@
+/* See LICENSE file for copyright and license details. */
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "util.h"
+
+extern char **environ;
+
+static void
+usage(void)
+{
+	eprintf("usage: %s [-i] [-u var] ... [var=value] ... [cmd [arg ...]]\n", argv0);
+}
+
+int
+main(int argc, char *argv[])
+{
+	int savederrno;
+
+	ARGBEGIN {
+	case 'i':
+		*environ = NULL;
+		break;
+	case 'u':
+		if (unsetenv(EARGF(usage())) < 0)
+			eprintf("unsetenv:");
+		break;
+	default:
+		usage();
+	} ARGEND
+
+	for (; *argv && strchr(*argv, '='); argc--, argv++)
+		putenv(*argv);
+
+	if (*argv) {
+		execvp(*argv, argv);
+		savederrno = errno;
+		weprintf("execvp %s:", *argv);
+		_exit(126 + (savederrno == ENOENT));
+	}
+
+	for (; *environ; environ++)
+		puts(*environ);
+
+	return fshut(stdout, "<stdout>");
+}