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/sha384.h

@@ -0,0 +1,16 @@
+/* public domain sha512 implementation based on fips180-3 */
+
+#include "sha512.h"
+
+#define sha384  sha512  /*struct*/
+
+enum { SHA384_DIGEST_LENGTH = 48 };
+
+/* reset state */
+void sha384_init(void *ctx);
+/* process message */
+#define sha384_update  sha512_update
+/* get message digest */
+/* state is ruined after sum, keep a copy if multiple sum is needed */
+/* part of the message might be left in s, zero it if secrecy is needed */
+void sha384_sum(void *ctx, uint8_t md[SHA384_DIGEST_LENGTH]);