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/head.c

@@ -0,0 +1,77 @@
+/* See LICENSE file for copyright and license details. */
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "util.h"
+
+static void
+head(FILE *fp, const char *fname, size_t n)
+{
+	char *buf = NULL;
+	size_t i = 0, size = 0;
+	ssize_t len;
+
+	while (i < n && (len = getline(&buf, &size, fp)) > 0) {
+		fwrite(buf, 1, len, stdout);
+		i += (len && (buf[len - 1] == '\n'));
+	}
+	free(buf);
+	if (ferror(fp))
+		eprintf("getline %s:", fname);
+}
+
+static void
+usage(void)
+{
+	eprintf("usage: %s [-num | -n num] [file ...]\n", argv0);
+}
+
+int
+main(int argc, char *argv[])
+{
+	size_t n = 10;
+	FILE *fp;
+	int ret = 0, newline = 0, many = 0;
+
+	ARGBEGIN {
+	case 'n':
+		n = estrtonum(EARGF(usage()), 0, MIN(LLONG_MAX, SIZE_MAX));
+		break;
+	ARGNUM:
+		n = ARGNUMF();
+		break;
+	default:
+		usage();
+	} ARGEND
+
+	if (!argc) {
+		head(stdin, "<stdin>", n);
+	} else {
+		many = argc > 1;
+		for (newline = 0; *argv; argc--, argv++) {
+			if (!strcmp(*argv, "-")) {
+				*argv = "<stdin>";
+				fp = stdin;
+			} else if (!(fp = fopen(*argv, "r"))) {
+				weprintf("fopen %s:", *argv);
+				ret = 1;
+				continue;
+			}
+			if (many) {
+				if (newline)
+					putchar('\n');
+				printf("==> %s <==\n", *argv);
+			}
+			newline = 1;
+			head(fp, *argv, n);
+			if (fp != stdin && fshut(fp, *argv))
+				ret = 1;
+		}
+	}
+
+	ret |= fshut(stdin, "<stdin>") | fshut(stdout, "<stdout>");
+
+	return ret;
+}