Building on Mac with --enable-clang-plugin

[Jonathan Watt]

The doc at:

https://developer.mozilla.org/en-US/docs/Mozilla/Testing/Clang_static_analysis

claims you just need to add --enable-clang-plugin to your mozconfig and build.
Unfortunately it doesn't seem to be that simple on Mac since Xcode doesn't come
with the 'llvm-config' binary:

configure: error: Cannot find an llvm-config binary for building a
clang plugin

(I notice Xcode also doesn't seem to have 'clang-tidy'.)

I tried using the prebuilt binaries from:

http://releases.llvm.org/download.html

which do have the needed binaries, but then I run into:

https://bugzilla.mozilla.org/show_bug.cgi?id=1348451

I tried various other things without success.

Can someone who's got this working on Mac summarize what they did? I'd be happy
to update the MDN wiki page once I have it working myself.

Cheers,
Jonathan