meson: disable x86 asm in fewer cases.

meson: disable x86 asm in fewer cases.

This patch allows building asm for x86 on x86_64 platforms, when the
operating system is the same. Previously cross compile always turned off
assembly. This allows using a cross file to cross compile x86 binaries
on x86_64 with asm.

This could probably be relaxed further thanks to meson's "exe_wrapper",
which is way to specify an emulator or compatibility layer (wine) that
can run the foreign binaries on the build system. Since the meson build
at this point only supports building on Linux I can't test this and I
don't want to write/enable code that cannot even be build tested.

v4: - set condition to build == x86_64 and host == x86 and
      build.system == host.system

Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>