The CMake function `get_effective_platform_for_triple` appears to only
be used in one location: from within `escape_path_for_xcode`.
The `get_effective_platform_for_triple` function's only purpose appears to be
to check whether `SWIFT_HOST_TRIPLE` contains the string "macos", and if not,
it emits an error.
However, because on macOS hosts the build-script-impl is responsible
for setting the `SWIFT_HOST_TRIPLE` variable, when `cmake -G Xcode` is invoked
directly to configure the Swift project, this variable is unset, and so
`get_effective_platform_for_triple` emits an error.
I considered two solutions:
1. Have `swift/CMakeLists.txt` set a default `SWIFT_HOST_TRIPLE`, as it
does for Linux. This would prevent `get_effective_platform_for_triple`
from emitting an error.
2. Remove `get_effective_platform_for_triple` altogether.
I chose (2) here. `get_effective_platform_for_triple` doesn't appear to
do anything besides restrict the host platform arbitrarily. If users
are somehow able to configure the project using `cmake -G Xcode` on
Linux, shouldn't the Swift's CMake allow them to do so?
Test plan:
1. Configure and build using Xcode and an in-tree Swift checkout.
2. Configure and build using `utils/build-script --xcode`.
Enable CMake policy CMP0057, which allows `if()` statements to use the `IN_LIST`
operator. In addition, simplify several `if()` statements that used the
`list(FIND ...)` operation instead.
Instead of overwriting all of the paths for the other build configurations with
the one that LLVM selected, I was resetting the path for LLVM's build
configuration over and over again. = /.
This fixes the issue.
As an additional fix, this moves the include of SwiftXcodeSupport to the one
place where its functionality is used, AddSwift.cmake. Keeping the include in
./CMakeLists.txt makes it seem like the functionality is needed there (when it
is not).
In a subsequent commit, I am going to refactor the xcode support I have been
adding to SwiftSharedCMakeConfig into this file and have SwiftSharedCMakeConfig
import it.
