Refactor libunwind to work on osx

[kangaroo]

Initial pass at OS X support.

It still unwinds on linux. It doesn't succeed on OS X yet, but its not failing to compile/crashing anymore.

Test:

basalt:debug plasma$ cat unw.cs 
 using System;

 class Program
    {
        static void A()
        {
            B();
        }

        static void B()
        {
            C();
        }

        static void C()
        {
            D();
        }

        static void D()
        {
            Console.WriteLine("About to unwind");
            var st = System.Environment.StackTrace;
            Console.WriteLine (st == null ? "null" : st);
            Console.WriteLine("Unwound");
        }

        static void Main(string[] args)
        {
            A();
        }
    }

Linux:

vagrant@vagrant-ubuntu-trusty-64:/vagrant/binaries/Product/amd64/debug$ uname -a
Linux vagrant-ubuntu-trusty-64 3.13.0-45-generic #74-Ubuntu SMP Tue Jan 13 19:36:28 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
vagrant@vagrant-ubuntu-trusty-64:/vagrant/binaries/Product/amd64/debug$ ./corerun -c . unw.exe 
About to unwind
   at System.Environment.GetStackTrace(Exception e, Boolean needFileInfo)
   at System.Environment.get_StackTrace()
   at Program.D()
   at Program.Main(String[] args)
Unwound

Mac:

basalt:debug plasma$ uname -a
Darwin basalt.local 14.1.0 Darwin Kernel Version 14.1.0: Mon Dec 22 23:10:38 PST 2014; root:xnu-2782.10.72~2/RELEASE_X86_64 x86_64
basalt:debug plasma$ ./corerun -c . unw.exe 
About to unwind

Unwound

[kangaroo]

@janvorli We've had some back and forth on this. Want me to rebase and squash it down?

[janvorli]

@kangaroo Yes please, that would be nice.

[kangaroo]

Rebased into 551c976

[janvorli]

LGTM

[janvorli]

@kangaroo Thank you very much for making it work on OSX!

[kangaroo]

@janvorli No problem. Do we need 2 core members to sign this PR? Since its not targeting master (I submitted this against your branch), should we merge into there and continue review there?

[janvorli]

I think we should merge right away and then I should reflect the feedback I got on my changes from @jkotas. But we'll have a cross platform weekly meeting in a minute, so I'll double check thatin there and will merge right after.

[kangaroo]

Alright, I'm rebasing the branch onto master currently anyways, so if that passes tests I'll push that up to this branch as a separate commit as well.

[kangaroo]

Build failure seems unrelated, something is flapping on windows.

[kangaroo]

@dotnet-bot test this please

[janvorli]

@mmitche There is something strange going on with the windows build. It fails with
C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\V120\BuildCustomizations\masm.targets(50,5): error MSB4175: The task factory "XamlTaskFactory" could not be loaded from the assembly "Microsoft.Build.Tasks.v4.0, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a". Could not find file 'C:\Windows\TEMP\qhmbsmpu.dll'
Which I don't see possibly related to @kangaroo's change.
Do you have any idea what could be causing that?

[mmitche]

taking a look now

[mmitche]

@kangaroo The failure doesn't appear on master on one of those machines that failed, so I don't think it's a machine issue. I'm checking the feature branch now.

[mmitche]

@dotnet-bot test this please

I've been unable to reproduce the failure on that machine...attempting to get some more data now.

[kangaroo]

@mmitche It was failing on DEBUG before, now RELEASE, and my patch doesn't touch windows. It seems to be flapping for some reason.

[mmitche]

@kangaroo Your patch does touch a few of the build files, probably from merges, so it's a possibility that that's related somehow. But when I checked out your branch I got none of those failures..

[mmitche]

@dotnet-bot test this please

[kangaroo]

@mmitche yeah thats from the master rebase

[mmitche]

@kangaroo @janvorli I can continue investigating tomorrow, I have to head out. Although Jan may have a different opinion, since this isn't a merge into master I'm okay with this being merged for now if it's not going to break his workflow.

[janvorli]

@mmitche, @kangaroo I was just going to write the same as Matt. This is our feature branch, so let's just merge the change in.

[kangaroo]

And now it passed :)