`SWIFT_BUILD_STATIC_STDLIB` is not mutually exclusive with
`SWIFT_BUILD_DYNAMIC_STDLIB`, and Linux sets both, so we can't use
`SWIFT_BUILD_STATIC_STDLIB` to conditionalise things.
The linker error about duplicate definitions for the threading error
handler was happening because we were forced to include the object
containing that symbol; moving it to another object should fix that.
And it turns out there's a way to get CMake to include the threading
object library only when building a shared object, so use that too.
rdar://90776105
`SWIFT_BUILD_STATIC_STDLIB` is not mutually exclusive with
`SWIFT_BUILD_DYNAMIC_STDLIB`, and Linux sets both, so we can't use
`SWIFT_BUILD_STATIC_STDLIB` to conditionalise things.
The linker error about duplicate definitions for the threading error
handler was happening because we were forced to include the object
containing that symbol; moving it to another object should fix that.
And it turns out there's a way to get CMake to include the threading
object library only when building a shared object, so use that too.
rdar://90776105
