We need to align TCB offset to the maximum alignment for TLS_TCB_AT_TP
targets, as _dl_allocate_tls_storage (in elf/dl-tls.c) does using
__libc_memalign and dl_tls_static_align.
[BZ #18383]
* csu/libc-tls.c (__libc_setup_tls) [TLS_TCB_AT_TP]: Align
TCB_OFFSET to MAX_ALIGN, not just TCBALIGN. Add comment.
* elf/Makefile (test-xfail-tst-tlsalign{,-static}): Remove
comment for i386/x86-64.
(test-xfail-tst-tlsalign-extern-static): Removed.