RFC: minimal backport of 8182299 build on OSX 10 + Xcode 8

[Simon Tooke]

Hello everyone,

I would like to make a somewhat controversial proposal: to backport the
minimal changes required to enable jdk8u to compile and run when built
with the latest macOS developer tools. 

I realize this falls outside of aph's guidelines of "bug fixes only,
(for now)" and in many ways is only a developer convenience, since I am
not advocating (at this time) for this build to become the default
supported for macOS [1].

There changes do not affect the current mac build, which requires an old
version of Xcode which doesn't run on modern releases of macOS, but they
make it much easier for macOS hackers to work with jdk8.

At this point, testing has been confined to bootstrapping the build with
a jdk8 built using this patch, and to using this build to build a
working Graal substrateVM.

My version of the backport limits the scope of the 8182299 patches to
the subset required to get the JDK up and running.  I don't propose
backporting any changes to remove Clang warnings, etc.  Because of that,
my changes are confined in scope.

Potential long term benefits (if this build does seem healthy enough for
production) are simplified macOS build platforms, a more modern compiler
and perhaps higher performance.

Bug: https://bugs.openjdk.java.net/browse/JDK-8182656

Webrev: http://cr.openjdk.java.net/~stooke/webrevs/xcodemacos.webrev/

Thanks for your time,

-Simon

[1] first, potentially removes support for macOS 10.8, second, needs
more testing.