Adopt javah deprecation

[Dmitry Samersoff]

Hi Everybody,

javah deprecated since jdk8 and completely removed in jdk11. So we
should replace javah with javac -h <directory> in graal/truffle build.

Below is the patch I proposed:

On MX side, always use javac -h .

On Graal side change com.oracle.truffle.nfi.native/Makefile
to collect generated headers on the fly.


https://github.com/dsamersoff/mx/commit/f55ba964e46aadb494280274c521a6853bfaef0d

https://github.com/dsamersoff/graal/commit/ed7ffedde748e5f10b241924ed0995f5916dbc4c


-Dmitry