x86, fpu, amd: Clear exceptions in AMD FXSAVE workaround

x86, fpu, amd: Clear exceptions in AMD FXSAVE workaround

Before we do an EMMS in the AMD FXSAVE information leak workaround we
need to clear any pending exceptions, otherwise we trap with a
floating-point exception inside this code.

Reported-by: halfdog <me@halfdog.net>
Tested-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/CA%2B55aFxQnY_PCG_n4=0w-VG=YLXL-yr7oMxyy0WU2gCBAf3ydg@mail.gmail.com
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
(cherry picked from commit 26bef1318adc1b3a530ecc807ef99346db2aa8b0)
[wt: in 2.6.32, patch applies to arch/x86/include/asm/i387.h. There's
 no static_cpu_has() so we use boot_cpu_has() like other kernels do
 with gcc3.
]
Signed-off-by: Willy Tarreau <w@1wt.eu>