Literal overflow warnings should only apply to decimal.

[mahkoh]

E.g. 0x8888i16 should not warn. Similar to binary operations | and &, hexadecimal, binary, and octal literals are often used to specify the concrete representation in memory whereas decimal literals are used to represent abstract values.

@pnkfelix @nikomatsakis

[theemathas]

Also note that -(0x8000i16) which evaluates to -32768 (hex: 0x8000i16, which is the minimum value of i16) currently does not warn.

[theemathas]

cc #22020