x86emul: fix test harness and fuzzer build dependencies

x86emul: fix test harness and fuzzer build dependencies

Commit fd35f32b4b ("tools/x86emul: Use struct cpuid_policy in the
userspace test harnesses") didn't account for the dependencies of
cpuid-autogen.h to potentially change between incremental builds. In
particular the harness has a "run" goal which is supposed to be usable
independently of the rest of the tools sub-tree building, and both the
harness and the fuzzer code are also supposed to be buildable
independently. Therefore a re-build of the generated header needs to be
triggered first, which is achieved by introducing a new top-level target
pattern (for just the "run" part for now).

Further cpuid.o did not have any dependencies added for it.

Finally, while at it, add a "run" target to the cpu-policy test harness.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>