[swift-dev] Please remove your Swift build directory

[Joe Groff]

> On May 31, 2016, at 10:20 AM, Joe Groff via swift-dev <swift-dev at swift.org> wrote:
> 
> 
>> 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.

New build-script also appears to pass some CMake variables that aren't used in the ninja configuration:

	-- Generating done
	CMake Warning:
	  Manually-specified variables were not used by the project:
	
	    SWIFT_BUILD_EXAMPLES
	    SWIFT_HOST_TRIPLE

-Joe