register as second parameter to the REGISTER macro.
* sysdeps/ia64/tls.h (DB_THREAD_SELF): Likewise.
* sysdeps/powerpc/tls.h (DB_THREAD_SELF): Likewise.
* sysdeps/sh/tls.h (DB_THREAD_SELF): Likewise.
* sysdeps/sparc/tls.h (DB_THREAD_SELF): Likewise.
* sysdeps/s390/tls.h (DB_THREAD_SELF): Pass __WORDSIZE as bit size
of thread register as second parameter to REGISTER macro in 64 case.