* sysdeps/i386/tls.h (TLS_DO_MODIFY_LDT): Rewrite asm to use %ebx

* sysdeps/i386/tls.h (TLS_DO_MODIFY_LDT): Rewrite asm to use %ebx

	optimally conditional on [__PIC__].
	(TLS_DO_SET_THREAD_AREA): New macro, implement inline syscall
	without touching errno, and use latest modify_ldt-like interface.
	(TLS_SETUP_GS_SEGMENT): Use that instead of INLINE_SYSCALL.
	* sysdeps/i386/useldt.h (DO_MODIFY_LDT): Set %gs in this macro.
	(DO_SET_THREAD_AREA): New macro, uses current syscall interface with
	existing %gs value as the segment to set.
	(INIT_THREAD_SELF): Rewritten using those.  Use set_thread_area only
	under [HAVE_TLS_SUPPORT] so we can rely on the initialization done
	by the first thread's early TLS setup.