macos: libcoreclr does not load with error "symbol not found: _clock_gettime" on 10.10/11

[natemcmaster]

libcoreclr.dylib fails to load with the following error:

dyld: Symbol not found: _clock_gettime
  Referenced from: /Users/asplab/.dotnet/shared/Microsoft.NETCore.App/2.0.0-beta-001808-00/libcoreclr.dylib (which was built for Mac OS X 10.12)
  Expected in: /usr/lib/libSystem.B.dylib

Repro
git clone https://github.com/aspnet/Options.git
dotnet restore
dotnet test test/Microsoft.Extensions.options.Test/Microsoft.Extensions.Options.Test.csproj

FYI you can also repro by executing ./build.sh with no args. At the time we hit this error, the script was pulling .NET Core CLI 2.0.0-preview1-005418 and Microsoft.NETCore.App 2.0.0-beta-001808-00.

System info
OSX 10.10.3

cc @jbagga

[gkhanna79]

Our CI and official build system has moved to OSX 10.12 and thus, you will need to move to 10.12 as well.

CC @Petermarcu

[natemcmaster]

So, OSX 10.11 support is being dropped in .NET Core 2.0?

Regardless, @BrennanConroy looks like our osx agents need an update. Just checked the docs and it looks like osx 10.10 was never officially supported by the runtime. The fact that it worked up until now was dumb luck.

[gkhanna79]

So, OSX 10.11 support is being dropped in .NET Core 2.0?

Yes, that is the current POR. I would suggest you have the machines updated across the board.

[BrennanConroy]

We have https://github.com/aspnet/Coherence-Signed/issues/317 looks like we should actually do it now

[natemcmaster]

Ok. @gkhanna79 feel free to close unless you want to use this to track follow up. We'll update aspnet build to a newer OS.