osmo_panic(): Annotate as __attribute__ ((noreturn))

In Change-Id I5a70eb65952cbc329bf96eacb428b07a9da32433 we redirected
all OSMO_ASSERT() via osmo_panic().  However, this caused various
applications to have build failures, as OSMO_ASSERT() now appeared
to be able to return to the call site.  Let's inform the compiler
explicitly that there's no return from osmo_panic().

Change-Id: I8adf4c7b0ee6a4581cef8dd4e9f6a1dfde70ee55

include/osmocom/core/panic.h

@@ -9,7 +9,7 @@
 /*! panic handler callback function type */
 typedef void (*osmo_panic_handler_t)(const char *fmt, va_list args);
 
-extern void osmo_panic(const char *fmt, ...);
+extern void osmo_panic(const char *fmt, ...) __attribute__ ((noreturn));
 extern void osmo_set_panic_handler(osmo_panic_handler_t h);
 
 /*! @} */

src/panic.c

@@ -27,6 +27,7 @@
  *  @{
  * \file panic.c */
 
+#include <unistd.h>
 #include <osmocom/core/panic.h>
 #include <osmocom/core/backtrace.h>
 
@@ -83,8 +84,14 @@ void osmo_panic(const char *fmt, ...)
 		osmo_panic_default(fmt, args);
 
 	va_end(args);
+
+	/* not reached, but make compiler believe we really never return */
+#ifndef PANIC_INFLOOP
+	exit(2342);
+#else
+	while (1) ;
+#endif
 }
- 
 
 /*! Set the panic handler
  *  \param[in] h New panic handler function