do not omit calls to empty methods which may trigger class initializatio...

...n

There's a small optimization in compileDirectInvoke which tries to
avoid generating calls to empty methods.  However, this causes
problems for code which uses such a call to ensure a class is
initialized -- if we omit that call, the class may not be
initialized and any side effects of that initialization may not
happen when the program expects them to.

This commit ensures that the compiler only omits empty method calls
when the target class does not need initialization.  It also removes
commented-out code in classpath-openjdk.cpp which was responsible for
loading libmawt proactively; that was a hack to get JogAmp to work
before we understood what the real problem was.