initcalls: Fix m68k build and possible buffer overflow

This patch fixes a build bug on m68k - gcc decides to emit a call to the
strlen library function, which we don't implement.

More importantly - my previous patch "init: don't lose initcall return
values" (commit e662e1cfd434aa234b72fbc781f1d70211cb785b) had introduced
potential buffer overflow by wrong calculation of string accumulator
size.

Use strlcat() instead, fixing both bugs.

Many thanks Andreas Schwab and Geert Uytterhoeven for helping
to catch and fix the bug.

Signed-off-by: Cyrill Gorcunov <[e-mail]>
Cc: Geert Uytterhoeven <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

init/main.c

···
 {
 	int count = preempt_count();
 	ktime_t t0, t1, delta;
-	char msgbuf[40];
+	char msgbuf[64];
 	int result;
 
 	if (initcall_debug) {
···
 		sprintf(msgbuf, "error code %d ", result);
 
 	if (preempt_count() != count) {
-		strncat(msgbuf, "preemption imbalance ", sizeof(msgbuf));
+		strlcat(msgbuf, "preemption imbalance ", sizeof(msgbuf));
 		preempt_count() = count;
 	}
 	if (irqs_disabled()) {
-		strncat(msgbuf, "disabled interrupts ", sizeof(msgbuf));
+		strlcat(msgbuf, "disabled interrupts ", sizeof(msgbuf));
 		local_irq_enable();
 	}
 	if (msgbuf[0]) {