kvm tools: Fix 32-bit build of the asm/system.h include

kvm tools: Fix 32-bit build of the asm/system.h include

Provide wrappers and other environmental dependencies that the
asm/system.h header file from hell needs to build fine in user-space.

Sidenote: right now alternative() defaults to the compatible, slightly
slower barrier instructions that work on all x86 systems.

If this ever shows up in profiles then kvm could provide an alternatives
patching machinery as well. Right now those instructions are emitted
into special sections and then discarded by the linker harmlessly.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Pekka Enberg <penberg@kernel.org>