perf bench mem: Prepare the x86-64 build for upstream memcpy_mcsafe() changes

perf bench mem: Prepare the x86-64 build for upstream memcpy_mcsafe() changes

The following upcoming upstream commit:

  92b0729c34ca ("x86/mm, x86/mce: Add memcpy_mcsafe()")

Adds _ASM_EXTABLE_FAULT(), which is not available in user-space
and breaks the build.

We don't really need _ASM_EXTABLE_FAULT() in user-space, so simply
wrap it to nothing.

Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Hitoshi Mitake <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Signed-off-by: Ingo Molnar <[email protected]>