utils: Move thread-safe strerror replacement to a separate file

For some utils _GNU_SOURCE might be needed but that conflicts with the
signature of strerror_r(3).

src/libstrongswan/utils/utils.c

@@ -303,84 +303,6 @@ char* tty_escape_get(int fd, tty_escape_t escape)
 	return "";
 }
 
-/**
- * The size of the thread-specific error buffer
- */
-#define STRERROR_BUF_LEN 256
-
-/**
- * Key to store thread-specific error buffer
- */
-static pthread_key_t strerror_buf_key;
-
-/**
- * Only initialize the key above once
- */
-static pthread_once_t strerror_buf_key_once = PTHREAD_ONCE_INIT;
-
-/**
- * Create the key used for the thread-specific error buffer
- */
-static void create_strerror_buf_key()
-{
-	pthread_key_create(&strerror_buf_key, free);
-}
-
-/**
- * Retrieve the error buffer assigned to the current thread (or create it)
- */
-static inline char *get_strerror_buf()
-{
-	char *buf;
-
-	pthread_once(&strerror_buf_key_once, create_strerror_buf_key);
-	buf = pthread_getspecific(strerror_buf_key);
-	if (!buf)
-	{
-		buf = malloc(STRERROR_BUF_LEN);
-		pthread_setspecific(strerror_buf_key, buf);
-	}
-	return buf;
-}
-
-#ifdef HAVE_STRERROR_R
-/*
- * Described in header.
- */
-const char *safe_strerror(int errnum)
-{
-	char *buf = get_strerror_buf(), *msg;
-
-#ifdef STRERROR_R_CHAR_P
-	/* char* version which may or may not return the original buffer */
-	msg = strerror_r(errnum, buf, STRERROR_BUF_LEN);
-#else
-	/* int version returns 0 on success */
-	msg = strerror_r(errnum, buf, STRERROR_BUF_LEN) ? "Unknown error" : buf;
-#endif
-	return msg;
-}
-#else /* HAVE_STRERROR_R */
-/* we actually wan't to call strerror(3) below */
-#undef strerror
-/*
- * Described in header.
- */
-const char *safe_strerror(int errnum)
-{
-	static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
-	char *buf = get_strerror_buf();
-
-	/* use a mutex to ensure calling strerror(3) is thread-safe */
-	pthread_mutex_lock(&mutex);
-	strncpy(buf, strerror(errnum), STRERROR_BUF_LEN);
-	pthread_mutex_unlock(&mutex);
-	buf[STRERROR_BUF_LEN - 1] = '\0';
-	return buf;
-}
-#endif /* HAVE_STRERROR_R */
-
-
 #ifndef HAVE_CLOSEFROM
 /**
  * Described in header.