[swift-dev] Please remove your Swift build directory

[Joe Groff]

> On May 31, 2016, at 9:37 AM, Dmitri Gribenko via swift-dev <swift-dev at swift.org> wrote:
> 
> Hi,
> 
> We have merged a CMake and build-script refactoring that requires a
> from-scratch build.  Trying to use an existing build directory will
> result in strange errors in the middle of the build.
> 
> Excuse me for the inconvenience.

This seems to have broken Xcode project generation, which in the default configuration now fails with:

	-- 
	CMake Error at CMakeLists.txt:702 (message):
	  Unknown SDKs:
	  IOS;IOS_SIMULATOR;TVOS;TVOS_SIMULATOR;WATCHOS;WATCHOS_SIMULATOR

Probably easy to work around by manually configuring out those SDKs, since Xcode projects don't support cross-building to begin with, but this used to just work.

-Joe