"javac -help "
helpfully lists the -h option, but the javac man pages included in openjdk do not.

  -d <directory> Specify where to place generated class files
  -s <directory> Specify where to place generated source files
  -h <directory> Specify where to place generated native header files

Documentation is expected to be very similar to -d and -s

Unfortunately there are multiple javac.1 files included in openjdk.