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/whoami.c

@@ -0,0 +1,37 @@
+/* See LICENSE file for copyright and license details. */
+#include <errno.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <pwd.h>
+
+#include "util.h"
+
+static void
+usage(void)
+{
+	eprintf("usage: %s\n", argv0);
+}
+
+int
+main(int argc, char *argv[])
+{
+	uid_t uid;
+	struct passwd *pw;
+
+	argv0 = *argv, argv0 ? (argc--, argv++) : (void *)0;
+
+	if (argc)
+		usage();
+
+	uid = geteuid();
+	errno = 0;
+	if (!(pw = getpwuid(uid))) {
+		if (errno)
+			eprintf("getpwuid %d:", uid);
+		else
+			eprintf("getpwuid %d: no such user\n", uid);
+	}
+	puts(pw->pw_name);
+
+	return fshut(stdout, "<stdout>");
+}