* path.cc (mount_info::read_cygdrive_info_from_registry): Use the user prefix

if it exists.
* sync.h (sync::init_lock): Declare new static member.
(sync::init()): Declare new static function.
* sync.cc (sync::init): Define.
(sync::init): Lock attempt to initialize a muto to stop multiple threads from
colliding.
* dcrt0.cc (dll_crt0_0): Initialize muto environment.

winsup/cygwin/path.cc

@@ -1956,6 +1956,7 @@ mount_info::read_cygdrive_info_from_registry ()
 	cygdrive_flags |= MOUNT_SYSTEM;
       slashify (cygdrive, cygdrive, 1);
       cygdrive_len = strlen (cygdrive);
+      break;
     }
 }