Allow annotation processing of class files in jtreg directives

When JSR 269 annotation processing was added to javac, javac gained the ability to operate directly on class files in addition to source files. That is, the file argument on the right hand side of the command line could be names of types, names that don't end in ".java". However, the @compile directive in jtreg checks and enforces that such non "*.java" command line arguments do not occur. To use the abilities of the platform (and to test javac operating on class files!), there should be some @compile-like directive which allows class file arguments. Keeping the check by default for @compiile is probably prudent, but something like "@compile/process" or "@process" should be supported.

Having such a feature would have greatly simplified testing of 6498938.