swift234

Fix eight Linux warnings.

Fix spurious docs warning that @in and @in_guaranteed should be ``fn``.

Add ``#ifdef SWIFT_OBJC_INTEROP`` to silence a -Wunused-function
on linux since that function is only used from within that #ifdef
elsewhere.

Fix three -Wunused-function warnings on linux.

Fix two -Wunreachable-code warnings on linux dealing with
SWIFT_HAVE_WORKING_STD_REGEX.