Support setting alignment on globals

Currently if one wants to set alignment on globals (either static or const) it needs to use a wrapper:

struct Aligned(u8);

static X: Aligned = Aligned(0);
const Y: Aligned = Aligned(0);

instead it would be nice to support align on static/const directly:

#[repr(align(8))] // or maybe #[align(8)]
static X: u8 = 0;
#[repr(align(8))] // or maybe #[align(8)]
const Y: u8 = 0;

Yes it needs a wrapper. The type contains its align. Calling a function that need align on a not-aligned struct is unsafe (and perhaps unsound)

if a function needs a u8, the function should not acquire the u8 is aligned, and if that function required an aligned item, it should not require u8 type directly in safe Rust.