How to indent on LOCK(); macro???

[Roy Smith]

I'm working on a project which uses a LOCK/END_LOCK macro pair for
mutex locking in C++ source files.  A typical section of code would
look like:

    LOCK (myDataLock)
        myData = foo;
    END_LOCK

How can I convince the indenting engine to treat the LOCK and END_LOCK
lines as beginning and ending blocks?

I'm running GNU Emacs 21.3.1.