Revert "x86/fpu: Use _Alignof to avoid undefined behavior in TYPE_ALIGN"

This reverts commit a00d020f which is
commit 55228db2697c09abddcb9487c3d9fa5854a932cd upstream.

_Alignof is not in the gcc version that the 4.19.y kernel still
supports (4.6), so this change needs to be reverted as it breaks the
build on those older compiler versions.

Reported-by: Michael Nies <michael.nies@netclusive.com>
Link: https://lore.kernel.org/r/HE1PR0902MB188277E37DED663AE440510BE1D99@HE1PR0902MB1882.eurprd09.prod.outlook.com
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217013


Cc: YingChi Long <me@inclyc.cn>
Cc: Borislav Petkov <bp@suse.de>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>