further use of _Noreturn, for non-plain-C functions

note that POSIX does not specify these functions as _Noreturn, because
POSIX is aligned with C99, not the new C11 standard. when POSIX is
eventually updated to C11, it will almost surely give these functions
the _Noreturn attribute. for now, the actual _Noreturn keyword is not
used anyway when compiling with a c99 compiler, which is what POSIX
requires; the GCC __attribute__ is used instead if it's available,
however.

in a few places, I've added infinite for loops at the end of _Noreturn
functions to silence compiler warnings. presumably
__buildin_unreachable could achieve the same thing, but it would only
work on newer GCCs and would not be portable. the loops should have
near-zero code size cost anyway.

like the previous _Noreturn commit, this one is based on patches
contributed by philomath.

include/assert.h

@@ -1,5 +1,12 @@
 #undef assert
 
+#if __STDC_VERSION__ >= 201112L
+#elif defined(__GNUC__)
+#define _Noreturn __attribute__((__noreturn__))
+#else
+#define _Noreturn
+#endif
+
 #ifdef NDEBUG
 #define	assert(x) (void)0
 #else
@@ -10,7 +17,7 @@
 extern "C" {
 #endif
 
-void __assert_fail (const char *, const char *, int, const char *);
+_Noreturn void __assert_fail (const char *, const char *, int, const char *);
 
 #ifdef __cplusplus
 }

include/err.h

@@ -1,6 +1,13 @@
 #ifndef _ERR_H
 #define _ERR_H
 
+#if __STDC_VERSION__ >= 201112L
+#elif defined(__GNUC__)
+#define _Noreturn __attribute__((__noreturn__))
+#else
+#define _Noreturn
+#endif
+
 #include <stdarg.h>
 
 #ifdef __cplusplus
@@ -12,10 +19,10 @@ void vwarn(const char *, va_list);
 void warnx(const char *, ...);
 void vwarnx(const char *, va_list);
 
-void err(int, const char *, ...);
-void verr(int, const char *, va_list);
-void errx(int, const char *, ...);
-void verrx(int, const char *, va_list);
+_Noreturn void err(int, const char *, ...);
+_Noreturn void verr(int, const char *, va_list);
+_Noreturn void errx(int, const char *, ...);
+_Noreturn void verrx(int, const char *, va_list);
 
 #ifdef __cplusplus
 }

include/pthread.h

@@ -10,6 +10,13 @@ extern "C" {
 #define __restrict
 #endif
 
+#if __STDC_VERSION__ >= 201112L
+#elif defined(__GNUC__)
+#define _Noreturn __attribute__((__noreturn__))
+#else
+#define _Noreturn
+#endif
+
 #define __NEED_time_t
 #define __NEED_clockid_t
 #define __NEED_struct_timespec
@@ -79,7 +86,7 @@ extern "C" {
 
 int pthread_create(pthread_t *__restrict, const pthread_attr_t *__restrict, void *(*)(void *), void *__restrict);
 int pthread_detach(pthread_t);
-void pthread_exit(void *);
+_Noreturn void pthread_exit(void *);
 int pthread_join(pthread_t, void **);
 
 #ifdef __GNUC__

include/setjmp.h

@@ -24,14 +24,14 @@ typedef struct {
 	unsigned long __ss[128/sizeof(long)];
 } sigjmp_buf[1];
 int sigsetjmp (sigjmp_buf, int);
-void siglongjmp (sigjmp_buf, int);
+_Noreturn void siglongjmp (sigjmp_buf, int);
 #endif
 
 
 #if defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) \
  || defined(_BSD_SOURCE)
 int _setjmp (jmp_buf);
-void _longjmp (jmp_buf, int);
+_Noreturn void _longjmp (jmp_buf, int);
 #endif
 
 

include/unistd.h

@@ -11,6 +11,13 @@ extern "C" {
 #define __restrict
 #endif
 
+#if __STDC_VERSION__ >= 201112L
+#elif defined(__GNUC__)
+#define _Noreturn __attribute__((__noreturn__))
+#else
+#define _Noreturn
+#endif
+
 #define STDIN_FILENO  0
 #define STDOUT_FILENO 1
 #define STDERR_FILENO 2
@@ -90,7 +97,7 @@ int execl(const char *, const char *, ...);
 int execvp(const char *, char *const []);
 int execlp(const char *, const char *, ...);
 int fexecve(int, char *const [], char *const []);
-void _exit(int);
+_Noreturn void _exit(int);
 
 pid_t getpid(void);
 pid_t getppid(void);