This removes the explicit tree structure reference in the stubs to
locate the shims. Instead, it expects that the `SwiftShims` directory
will be added to the header search path.
Use the wrapper for the CC adjustment as on Windows x86, the destructor
needs to be `__stdcall`. This would fail otherwise with the following:
```
D:\a\1\s\swift\stdlib\public\stubs\ThreadLocalStorage.cpp(86,18): error: no matching function for call to '_stdlib_thread_key_create'
int result = SWIFT_THREAD_KEY_CREATE(&key, [](void *pointer) {
^~~~~~~~~~~~~~~~~~~~~~~
D:\a\1\s\swift\stdlib\public\stubs/../runtime/ThreadLocalStorage.h(96,35): note: expanded from macro 'SWIFT_THREAD_KEY_CREATE'
^~~~~~~~~~~~~~~~~~~~~~~~~
D:\a\1\s\swift\include\swift/Basic/Lazy.h(42,27): note: expanded from macro 'SWIFT_ONCE_F'
::std::call_once(TOKEN, FUNC, CONTEXT)
^~~~
D:\a\1\s\swift\stdlib\public\stubs\ThreadLocalStorage.cpp(43,1): note: candidate function not viable: no known conversion from '(lambda at D:\a\1\s\swift\stdlib\public\stubs\ThreadLocalStorage.cpp:85:3)' to '__swift_thread_key_destructor _Nullable' (aka 'void (*)(void *) __attribute__((stdcall))') for 2nd argument
_stdlib_thread_key_create(__swift_thread_key_t * _Nonnull key,
^
```
The mapping of the return value of the `FlsAlloc` was flipped resulting
in the failure of the TLS key creation. The test suite would fail to
generate the TLS key resulting in failures.
Due to the build ordering, I didn't notice this earlier. The inclusion
of the header would define the guard, preventing the needed definitions.
Unconditionally define the functions to ensure that they are available.
Fix syntactic issues in the swift runtime build from the recent TLS changes.
Move the helper definitions into the TLS stubs rather than emitting them
everywhere. This allows the runtime to build again on Windows.
