Avoid redefinition of _XOPEN_SOURCE

@@ -19,7 +19,9 @@
 #include <sys/types.h>
 #include <stdlib.h>
 #include <stdio.h>
-#define _XOPEN_SOURCE
+#ifndef _XOPEN_SOURCE
+# define _XOPEN_SOURCE
+#endif
 #include <unistd.h>
 #include <pwd.h>
 #include <errno.h>

@@ -82,7 +82,7 @@ static struct _record _imap_record =
    via the register entry/record.  */
 record_t imap_record = &_imap_record;
 
-#ifndef HAVE_DECL_STRTOK_R
+#ifndef HAVE_STRTOK_R
 char *strtok_r                      (char *, const char *, char **);
 #endif
 

@@ -40,7 +40,9 @@
 
 #ifdef WITH_PTHREAD
 # ifdef HAVE_PTHREAD_H
-#  define _XOPEN_SOURCE  500
+#  ifndef _XOPEN_SOURCE
+#   define _XOPEN_SOURCE  500
+#  endif
 #  include <pthread.h>
 # endif
 #endif

@@ -31,7 +31,9 @@
 
 #ifdef WITH_PTHREAD
 # ifdef HAVE_PTHREAD_H
-#  define _XOPEN_SOURCE  500
+#  ifndef _XOPEN_SOURCE
+#   define _XOPEN_SOURCE  500
+#  endif
 #  include <pthread.h>
 # endif
 #endif

@@ -38,7 +38,9 @@
 
 #ifdef WITH_PTHREAD
 # ifdef HAVE_PTHREAD_H
-#  define _XOPEN_SOURCE  500
+#  ifndef _XOPEN_SOURCE
+#   define _XOPEN_SOURCE  500
+#  endif
 #  include <pthread.h>
 # endif
 #endif