Move the TinyCC/Windows ARM64 Interlocked workaround from the semlock call site into the bundled WinAPI header. This keeps tcc.h using the normal Interlocked API while avoiding unresolved Interlocked imports when tcc -run self-compiles on Windows ARM64.
Update lib/bt-exe.c as well so its ARM64 runtime object does not define a second InterlockedExchange fallback now provided by winnt.h.
