Try to fix FreeBSD build by avoiding name conflict

ext/journald_native/journald_native.c

@@ -92,7 +92,7 @@ static VALUE jdl_native_send(int argc, VALUE* argv, VALUE self)
     }
 
     /* allocate memory after all checks to avoid possible memory leak */
-    struct iovec* msgs = xcalloc(argc, sizeof(struct iovec));
+    iovec_t* msgs = xcalloc(argc, sizeof(iovec_t));
 
     for (int i = 0; i < argc; i++) {
         VALUE v = argv[i];

ext/journald_native/sd_journal.h

@@ -53,6 +53,9 @@
         /* include systemd-journal headers */
         #include <systemd/sd-journal.h>
 
+        /* use alias for iovec to avoid name conflicts in dummy version*/
+        typedef struct iovec iovec_t;
+
     #else
 
         #define JOURNALD_NATIVE_SD_JOURNAL_DUMMY true

ext/journald_native/sd_journal_dummy.h

@@ -21,22 +21,26 @@
 
 #include <stdlib.h>
 
-/* syslog constants */
-#define LOG_EMERG   0
-#define LOG_ALERT   1
-#define LOG_CRIT    2
-#define LOG_ERR     3
-#define LOG_WARNING 4
-#define LOG_NOTICE  5
-#define LOG_INFO    6
-#define LOG_DEBUG   7
+#ifndef LOG_EMERG
+    /* syslog constants */
+    #define LOG_EMERG   0
+    #define LOG_ALERT   1
+    #define LOG_CRIT    2
+    #define LOG_ERR     3
+    #define LOG_WARNING 4
+    #define LOG_NOTICE  5
+    #define LOG_INFO    6
+    #define LOG_DEBUG   7
+#endif
+
+typedef struct jdn_dummy_iovec iovec_t;
 
 /* iovec */
-struct iovec {
+struct jdn_dummy_iovec {
     void  *iov_base;    /* Starting address */
     size_t iov_len;     /* Number of bytes to transfer */
 };
 
 inline int sd_journal_print(int priority, const char *format, ...)  { return 0; }
-inline int sd_journal_sendv(const struct iovec *iov, int n)         { return 0; }
+inline int sd_journal_sendv(const iovec_t *iov, int n)              { return 0; }
 inline int sd_journal_perror(const char *message)                   { return 0; }