add missing header <thread>

building using musl fails due to missing defintions:

```
Source/Tools/LinuxEmulation/LinuxSyscalls/Syscalls.cpp:913:23: error: no member named 'sleep_for' in namespace 'std::this_thread'
  913 |     std::this_thread::sleep_for(std::chrono::milliseconds {10});
      |                       ^~~~~~~~~
1 error generated.
```

Signed-off-by: Pepper Gray <hello@peppergray.xyz>

Source/Tools/LinuxEmulation/LinuxSyscalls/Syscalls.cpp

@@ -60,6 +60,7 @@ $end_info$
 #include <syscall.h>
 #include <sys/mman.h>
 #include <sys/utsname.h>
+#include <thread>
 #include <unistd.h>
 
 namespace FEX::HLE {