[Threading][TSan] Fix builds where TSan isn't supported.

On builds where TSan isn't supported, don't include any code in
ThreadSanitizer.cpp.

rdar://110665213

include/swift/Threading/ThreadSanitizer.h

@@ -25,6 +25,9 @@
 namespace swift {
 
 #if defined(_WIN32) || defined(__wasi__) || !__has_include(<dlfcn.h>)
+
+#define SWIFT_THREADING_TSAN_SUPPORT 0
+
 namespace tsan {
 
 inline bool enabled() { return false; }
@@ -34,6 +37,8 @@ template <typename T> T *release(T *ptr) { return ptr; }
 } // namespace tsan
 #else
 
+#define SWIFT_THREADING_TSAN_SUPPORT 1
+
 // If we're static linking to libswiftThreading.a, these symbols can come
 // from there.  If, on the other hand, we're dynamically linked, we want
 // to get them from libswiftCore.dylib instead.