jdk10 on macOS

[Alan Snyder]

I am trying to build jdk10 on macOS 10.12.6. I got the basic build to work, but some tests fail.

Most of the test failures complain about not finding jasm or jcoder. This is odd because I downloaded jtreg-4.2-b11, which includes these classes, and the classpath appears to be correct in the log.

I got an error from StringPlatformChars, which could find native code. Could be the same jasm problem but not reported as such.

I got an error from NewUnsafeString, did not use provided string.