Handling of the unary_minus for the untyped unsigned literals.

[flysand7]

The following sif code:

a: uint = -0xFFFF_FFFF_FFFF_FFFF;
printa(a);

Prints out 0 to the screen.

Note: In checker.cpp, line 2822 we assign a negative version of int, f32 and f64 values to the result_operand. The uint_value stays at zero. Either an error should be printed or the behaviour in this case should be more defined (e.g. performing the minus as if on signed integer)