[klibc] dash: shell: Fix clang warnings about format string

Build with clang results in some warnings about using a non-string
literal for a format string.

-----------------------------------------------------------------------
usr/dash/jobs.c:429:23: warning: format string is not a string literal (potentially insecure) [-Wformat-security]
                col = fmtstr(s, 32, strsignal(st));
                                    ^~~~~~~~~~~~~
usr/dash/jobs.c:429:23: note: treat the string as an argument to avoid this
                col = fmtstr(s, 32, strsignal(st));
                                    ^
                                    "%s",
-----------------------------------------------------------------------

Signed-off-by: Bill Wendling <morbo@google.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
diff --git a/usr/dash/jobs.c b/usr/dash/jobs.c
index b9ff140..f027cc1 100644
--- a/usr/dash/jobs.c
+++ b/usr/dash/jobs.c
@@ -426,7 +426,7 @@
 				goto out;
 #endif
 		}
-		col = fmtstr(s, 32, strsignal(st));
+		col = fmtstr(s, 32, "%s", strsignal(st));
 #ifdef WCOREDUMP
 		if (WCOREDUMP(status)) {
 			col += fmtstr(s + col, 16, " (core dumped)");