include/posix: rearrange for standard use of extern "C"

Consistently place C++ use of extern "C" after all include directives,
within the negative branch of _ASMLANGUAGE if used.

Background from issue #17997:

Declarations that use C linkage should be placed within extern "C"
so the language linkage is correct when the header is included by
a C++ compiler.

Similarly #include directives should be outside the extern "C" to
ensure the language-specific default linkage is applied to any
declarations provided by the included header.

See: https://en.cppreference.com/w/cpp/language/language_linkage
Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>

include/posix/arpa/inet.h

@@ -6,12 +6,12 @@
 #ifndef ZEPHYR_INCLUDE_POSIX_ARPA_INET_H_
 #define ZEPHYR_INCLUDE_POSIX_ARPA_INET_H_
 
+#include <net/socket.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#include <net/socket.h>
-
 static inline char *inet_ntop(sa_family_t family, const void *src, char *dst,
 			      size_t size)
 {

include/posix/dirent.h

@@ -6,16 +6,16 @@
 #ifndef ZEPHYR_INCLUDE_POSIX_DIRENT_H_
 #define ZEPHYR_INCLUDE_POSIX_DIRENT_H_
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <limits.h>
 #include "posix_types.h"
 
 #ifdef CONFIG_POSIX_FS
 #include <fs/fs.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 typedef void DIR;
 
 struct dirent {
@@ -28,10 +28,10 @@ extern DIR *opendir(const char *dirname);
 extern int closedir(DIR *dirp);
 extern struct dirent *readdir(DIR *dirp);
 
-#endif
-
 #ifdef __cplusplus
 }
 #endif
 
+#endif /* CONFIG_POSIX_FS */
+
 #endif	/* ZEPHYR_INCLUDE_POSIX_DIRENT_H_ */

include/posix/netdb.h

@@ -6,12 +6,12 @@
 #ifndef ZEPHYR_INCLUDE_POSIX_NETDB_H_
 #define ZEPHYR_INCLUDE_POSIX_NETDB_H_
 
+#include <net/socket.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#include <net/socket.h>
-
 #define addrinfo zsock_addrinfo
 
 static inline int getaddrinfo(const char *host, const char *service,

include/posix/posix_types.h

@@ -7,16 +7,16 @@
 #ifndef ZEPHYR_INCLUDE_POSIX_SYS_TYPES_H_
 #define ZEPHYR_INCLUDE_POSIX_SYS_TYPES_H_
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #ifndef CONFIG_ARCH_POSIX
 #include <sys/types.h>
 #endif
 
 #include <kernel.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 typedef unsigned long useconds_t;
 
 /* time related attributes */

include/posix/pthread_key.h

@@ -7,14 +7,14 @@
 #ifndef ZEPHYR_INCLUDE_POSIX_PTHREAD_KEY_H_
 #define ZEPHYR_INCLUDE_POSIX_PTHREAD_KEY_H_
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #ifdef CONFIG_PTHREAD_IPC
 #include <sys/slist.h>
 #include <zephyr/types.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 typedef u32_t pthread_once_t;
 
 /* pthread_key */

include/posix/semaphore.h

@@ -6,13 +6,13 @@
 #ifndef ZEPHYR_INCLUDE_POSIX_SEMAPHORE_H_
 #define ZEPHYR_INCLUDE_POSIX_SEMAPHORE_H_
 
+#include <posix/time.h>
+#include "posix_types.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#include <posix/time.h>
-#include "posix_types.h"
-
 int sem_destroy(sem_t *semaphore);
 int sem_getvalue(sem_t *restrict semaphore, int *restrict value);
 int sem_init(sem_t *semaphore, int pshared, unsigned int value);

include/posix/signal.h

@@ -6,12 +6,12 @@
 #ifndef ZEPHYR_INCLUDE_POSIX_SIGNAL_H_
 #define ZEPHYR_INCLUDE_POSIX_SIGNAL_H_
 
+#include "posix_types.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#include "posix_types.h"
-
 #ifndef SIGEV_NONE
 #define SIGEV_NONE 1
 #endif

include/posix/sys/socket.h

@@ -6,13 +6,13 @@
 #ifndef ZEPHYR_INCLUDE_POSIX_SYS_SOCKET_H_
 #define ZEPHYR_INCLUDE_POSIX_SYS_SOCKET_H_
 
+#include <sys/types.h>
+#include <net/socket.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#include <sys/types.h>
-#include <net/socket.h>
-
 static inline int socket(int family, int type, int proto)
 {
 	return zsock_socket(family, type, proto);

include/posix/time.h

@@ -6,10 +6,6 @@
 #ifndef ZEPHYR_INCLUDE_POSIX_TIME_H_
 #define ZEPHYR_INCLUDE_POSIX_TIME_H_
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #ifdef CONFIG_NEWLIB_LIBC
 /* Kludge to support outdated newlib version as used in SDK 0.10 for Xtensa */
 #include <newlib.h>
@@ -17,20 +13,30 @@ extern "C" {
 #ifdef __NEWLIB__
 /* Newever Newlib 3.x+ */
 #include <sys/_timespec.h>
-#else
+#else /* __NEWLIB__ */
 /* Workaround for older Newlib 2.x, as used by Xtensa. It lacks sys/_timeval.h,
  * so mimic it here.
  */
 #include <sys/types.h>
 #ifndef __timespec_defined
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 struct timespec {
 	time_t tv_sec;
 	long tv_nsec;
 };
-#endif
+
+#ifdef __cplusplus
+}
 #endif
 
-#else
+#endif /* __timespec_defined */
+#endif /* __NEWLIB__ */
+
+#else /* CONFIG_NEWLIB_LIBC */
 /* Not Newlib */
 #include <sys/_timespec.h>
 #endif /* CONFIG_NEWLIB_LIBC */
@@ -44,10 +50,19 @@ struct timespec {
  */
 #if !defined(__NEWLIB_H__) || (__NEWLIB__ >= 3) || \
     (__NEWLIB__ == 2  && __NEWLIB_MINOR__ >= 2)
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 struct itimerspec {
 	struct timespec it_interval;  /* Timer interval */
 	struct timespec it_value;     /* Timer expiration */
 };
+#ifdef __cplusplus
+}
+#endif
+
 #endif
 
 #include <kernel.h>
@@ -55,6 +70,10 @@ struct itimerspec {
 #include "posix_types.h"
 #include <posix/signal.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #ifndef CLOCK_REALTIME
 #define CLOCK_REALTIME 0
 #endif

include/posix/unistd.h

@@ -6,10 +6,6 @@
 #ifndef ZEPHYR_INCLUDE_POSIX_UNISTD_H_
 #define ZEPHYR_INCLUDE_POSIX_UNISTD_H_
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include "posix_types.h"
 #include "sys/stat.h"
 #ifdef CONFIG_NETWORKING
@@ -20,6 +16,10 @@ extern "C" {
 #ifdef CONFIG_POSIX_API
 #include <fs/fs.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /* File related operations */
 extern int close(int file);
 extern ssize_t write(int file, const void *buffer, size_t count);