errno.h header is required now that errno is a per-thread variable.
"undefined symbol 'errno'" at runtime with dlopen()'d modules.

Index: backend/snapscan-mutex.c
--- backend/snapscan-mutex.c.orig
+++ backend/snapscan-mutex.c
@@ -67,6 +67,7 @@ static void snapscani_mutex_unlock(snapscan_mutex_t* a
 
 #elif defined USE_PTHREAD || defined HAVE_OS2_H
 
+#include <errno.h>
 #include <pthread.h>
 #define snapscan_mutex_t pthread_mutex_t