Try to make nasm_assert() do a static assert if the argument can be
evaluated at compile time by any particular compiler. We also provide
nasm_try_static_assert() which will assert a compile-time expression
if and only if we can determine we have a constant at compile time
*and* we know that the compiler has a way to handle it.
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>