support 64 bit retval for stub

[Angelo942]

Description

The return (int) X command in gdb only sets the 4 lowest bytes of the return register. For example if rax was -1, a return int 0 would leave us with 0xffffffff000000 instead of 0x0.

This patch makes StubBreakpoint check for the register size and executes return (int) or return (long) accordingly.

Checklist

• My code follows the code style of this project.
• My change includes a change to the documentation, if required.
• If my change adds new code, adequate tests have been added.
• I have read and agree to the CONTRIBUTING document.

[hugsy]

Great catch!