Implement quick_exit() / at_quick_exit() from C++11 / C1x. Also add a

__noreturn macro and modify the other exiting functions to use it.

The __noreturn macro, unlike __dead2, must be used BEFORE the function.
This is in line with the C and C++ specifications that place _Noreturn (c1x)
and [[noreturn]] (C++11) in front of the functions.  As with __dead2, this
macro falls back to using the GCC attribute.

Unfortunately, clang currently sets the same value for the C version macro
in C99 and C1x modes, so these functions are hidden by default.  At some
point before 10.0, I need to go through the headers and clean up the C1x /
C++11 visibility.

Reviewed by:	brooks (mentor)

1 files changed, 11 insertions, 0 deletions

diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h
index 495daf28e52e..ca485b3dcb91 100644
--- a/sys/sys/cdefs.h
+++ b/sys/sys/cdefs.h
@@ -218,6 +218,17 @@
 #endif
 #endif
 
+
+#if defined(__cplusplus) && __cplusplus >= 201103L
+#define	__noreturn		[[noreturn]]
+#elif defined(__STDC_VERSION__) && __STDC_VERSION__ > 201000L
+#define	__noreturn		_Noreturn
+#elif defined(__GNUC__)
+#define	__noreturn		__attribute__((__noreturn__))
+#else
+#define	__noreturn
+#endif
+
 #if __GNUC_PREREQ__(2, 96)
 #define	__malloc_like	__attribute__((__malloc__))
 #define	__pure		__attribute__((__pure__))