Link against pthread

This is required by gccgo because of the pthread_mutex_trylock symbol.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>

sqlite3.go

@@ -9,6 +9,7 @@ package sqlite3
 #cgo CFLAGS: -std=gnu99
 #cgo CFLAGS: -DSQLITE_ENABLE_RTREE -DSQLITE_THREADSAFE
 #cgo CFLAGS: -DSQLITE_ENABLE_FTS3 -DSQLITE_ENABLE_FTS3_PARENTHESIS
+#cgo LDFLAGS: -lpthread
 #include <sqlite3-binding.h>
 #include <stdlib.h>
 #include <string.h>