BUILD: bug: Fix error when compiling with -DDEBUG_STRICT_NOCRASH

ha_backtrace_to_stderr() must be declared in CRASH_NOW() macro whe HAProxy
is compiled with DEBUG_STRICT_NOCRASH. Otherwise an error is reported during
compilation:

include/haproxy/bug.h:58:26: error: implicit declaration of function ‘ha_backtrace_to_stderr’ [-Werror=implicit-function-declaration]
   58 | #define CRASH_NOW() do { ha_backtrace_to_stderr(); } while (0)

This patch must be backported as far as 2.4.

(cherry picked from commit d6ae912b04a38a544b2d37f549c7f86ae51e929c)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 9562b42de844f31225132ac97d1b7c5cee96a5d9)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/include/haproxy/bug.h b/include/haproxy/bug.h
index 7a2fa81..13815fe 100644
--- a/include/haproxy/bug.h
+++ b/include/haproxy/bug.h
@@ -55,7 +55,7 @@
 #if defined(DEBUG_STRICT)
 #define CRASH_NOW() ABORT_NOW()
 #else
-#define CRASH_NOW() do { ha_backtrace_to_stderr(); } while (0)
+#define CRASH_NOW() do { extern void ha_backtrace_to_stderr(void); ha_backtrace_to_stderr(); } while (0)
 #endif
 
 #define BUG_ON(cond) _BUG_ON(cond, __FILE__, __LINE__)