Hello,

I recently tried to build uclibc-ng configured with NPTL posix threads implementation for x86_64 system. Build fails, which I believe is a bug.

The error occurs when compiling `libpthread/nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S`, it takes the false branch in

```

#if USE___THREAD

...

#else

...

#endif

```

which contains #error preprocessor directive.

I tried to understand why it happens. Turns out the `USE___THREAD` macro is not defined when compiling this file and false branch in always taken. This macro is defined in tls.h, however this header files in not included directly or indirectly.

This issue should affect all assembler code in `libpthread/nptl/sysdeps/unix/sysv/linux/x86_64` since it all have preprocessor conditions depending on `USE___THREAD` macro.

Directly including tls.h fixes the build error.

- Kirill Makurin