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/which.c

@@ -0,0 +1,101 @@
+/* See LICENSE file for copyright and license details. */
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#include <fcntl.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "util.h"
+
+static int aflag;
+
+static int
+canexec(int fd, const char *name)
+{
+	struct stat st;
+
+	if (fstatat(fd, name, &st, 0) < 0 || !S_ISREG(st.st_mode))
+		return 0;
+	return faccessat(fd, name, X_OK, AT_EACCESS) == 0;
+}
+
+static int
+which(const char *path, const char *name)
+{
+	char *ptr, *p;
+	size_t i, len;
+	int dirfd, found = 0;
+
+	if (strchr(name, '/')) {
+		found = canexec(AT_FDCWD, name);
+		if (found)
+			puts(name);
+		return found;
+	}
+
+	ptr = p = enstrdup(3, path);
+	len = strlen(p);
+	for (i = 0; i < len + 1; i++) {
+		if (ptr[i] != ':' && ptr[i] != '\0')
+			continue;
+		ptr[i] = '\0';
+		if ((dirfd = open(p, O_RDONLY)) >= 0) {
+			if (canexec(dirfd, name)) {
+				found = 1;
+				fputs(p, stdout);
+				if (i && ptr[i - 1] != '/')
+					fputc('/', stdout);
+				puts(name);
+			}
+			close(dirfd);
+			if (!aflag && found)
+				break;
+		}
+		p = ptr + i + 1;
+	}
+	free(ptr);
+
+	return found;
+}
+
+static void
+usage(void)
+{
+	eprintf("usage: %s [-a] name ...\n", argv0);
+}
+
+int
+main(int argc, char *argv[])
+{
+	char *path;
+	int found = 0, foundall = 1;
+
+	ARGBEGIN {
+	case 'a':
+		aflag = 1;
+		break;
+	default:
+		usage();
+	} ARGEND
+
+	if (!argc)
+		usage();
+
+	if (!(path = getenv("PATH")))
+		enprintf(3, "$PATH is not set\n");
+
+	for (; *argv; argc--, argv++) {
+		if (which(path, *argv)) {
+			found = 1;
+		} else {
+			weprintf("%s: not an external command\n", *argv);
+			foundall = 0;
+		}
+	}
+
+	return found ? foundall ? 0 : 1 : 2;
+}