Because the target/i386/hvf/meson.build rule culls hvf support
on non-Darwin systems, a --enable-hvf build is succeeding.
To fix this, just try the compilation test every time someone
passes --enable-hvf.

Reported-by: Christophe de Dinechin <dinechin@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>