Move the generate backtrace call from MSGB_ABORT to osmo_panic handler

This has two benefits:
 - All people calling osmo_panic() will have the backtrace
 - It makes the thing build in 'target' mode in osmocom-bb

And one downside:
 - The osmo_panic handler is now in the backtrace
(I can live with that :)

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

include/osmocore/msgb.h

@@ -62,9 +62,7 @@ extern void msgb_reset(struct msgb *m);
 
 #ifdef MSGB_DEBUG
 #include <osmocore/panic.h>
-#include <osmocore/gsm_utils.h>
 #define MSGB_ABORT(msg, fmt, args ...) do {		\
-	generate_backtrace();				\
 	osmo_panic("msgb(%p): " fmt, msg, ## args);	\
 	} while(0)
 #else

src/panic.c

@@ -20,6 +20,7 @@
  *
  */
 
+#include <osmocore/gsm_utils.h>
 #include <osmocore/panic.h>
 
 #include "../config.h"
@@ -36,6 +37,7 @@ static osmo_panic_handler_t osmo_panic_handler = (void*)0;
 static void osmo_panic_default(const char *fmt, va_list args)
 {
 	vfprintf(stderr, fmt, args);
+	generate_backtrace();
 	abort();
 }