swift234

[cmake] Rename SWIFT_BUILD_TOOLS => SWIFT_INCLUDE_TOOLS

In LLVM, the convention is that *_INCLUDE_* means that cmake will generate
targets but says nothing about whether or not something will be built by default
or not. This means that as far as cmake is concerned, those targets do not
exist.

On the other hand, *_BUILD_* determines whether or not a class of things is a
dependency of the "all" target. Of course this implies that *_BUILD_* implies
that *_INCLUDE_* must be set to TRUE.

Currently SWIFT_BUILD_TOOLS is implemented like a *_INCLUDE_* option, so change
its name to SWIFT_INCLUDE_TOOLS.