Assembly builtins: signed and unsigned decimal printing.

[AndreasKrall]

Currently we only support a signed assembly printing function called decimal. We must support both the printing of signed and unsigned values. Currently the only way to support unsigned printing is to cast the printed value to an unsigned which is at least one bit bigger than the current value. I propose to support two different versions of decimal for signed and unsigned printing. We need to find suitable names. Suggestions are (please add further suggestions):

Sdecimal/Udecimal
decimalS/decimalU
sint/uint
sdec/udec

My preference is sdec/udec.
hex and bin will always interpreted as unsigned values.
Currently there are known errors in the RISC-V and AArch64 spec which have to be fixed after the new builtin versions are implemented.

[AndreasKrall]

In the meeting we agreed to use sdec/udec and keep for some time decimal as synonym to sdec to avoid breaking existing tests.