Fix iOS and Android builds

[bwrsandman]

Currently on travis, the iOS and Android builds are failing.
These should be fixed and their tests should be re-enabled.

• Android is failing because sdkmanager cannot find lldb 3.1 Error: Failed to find package lldb;3.1
• iOS is failing because it cannot find a Quartz Core header: fatal error: 'QuartzCore/CAMetalLayer.h' file not found

[JonnyPtn]

Kind of expected if we merge things that are broken...

The issue should be fixed by using Xcode 11, just need to make sure we don't merge broken stuff again in future?

[widberg]

https://stackoverflow.com/questions/24145101/quartzcore-cametallayer-h-file-not-found looks like a problem with the CI environment not being setup to use an iOS simulator that supports CAMetalLayer rather than a problem with the project code.

[JonnyPtn]

And before Xcode 11 there is no iOS simulator that supports metal. This issue was brought in when the bgfx submodules were updated without testing