This fixes C/gnu99/combo_load_mode.c, C/gnu99/computed_goto.c, C/gnu99/ijmp.c, C/gnu99/vlabel2.c and C/gnu99/vlabel3.c.

This fixes C/gnu99/combo_load_mode.c, C/gnu99/computed_goto.c, C/gnu99/ijmp.c, C/gnu99/vlabel2.c and C/gnu99/vlabel3.c.

With base the displacement may be a single byte.

'mov $~0x80000000, %r; ror x, %r' is shorter than 'mov $0x80000000, %r; shr x, %r; not %r'.

'mov $~1, %r; rol x, %r' is shorter than 'mov $1, %r; shl x, %r; not %r'.

'thunk' is the current and default style to get the ip.
'pop' is the old way using 'call base; base: pop %reg'.

This makes them easier to read and avoids markdown interpreting __xxx__
as bold.

Now every bit in the public API is documented so we can enable doxygen
warnings for undocumented members.