ITS#8612 Fix Solaris builds with liblmdb

This patch fixes liblmdb builds on Solaris and derivatives by defining
_POSIX_PTHREAD_SEMANTICS

libraries/liblmdb/mdb.c

@@ -142,6 +142,10 @@ typedef SSIZE_T	ssize_t;
 /* Most platforms have posix_memalign, older may only have memalign */
 #define HAVE_MEMALIGN	1
 #include <malloc.h>
+/* On Solaris, we need the POSIX sigwait function */
+#if defined (__sun)
+# define _POSIX_PTHREAD_SEMANTICS	1
+#endif
 #endif
 
 #if !(defined(BYTE_ORDER) || defined(__BYTE_ORDER))