x86-frame-lower: moved max align logic to new function getMaxAlign()

Segmented stack implementation need the max align logic and there was also code
duplication that had (probably unintentional) differences.
seg-stacks: special fx saving prologue generation for fx passing functions

In librcd the default morestack implementation will destroy the floating point
and other extended registers so a slower form of morestack is used which saves
and restores those when context switching. Instead of using the slower variant
for all functions we detect what functions has them in their argument list or
return value, so the slower variant is only used for those special functions.
seg-stacks: fix stack alloc not including space wasted on alignment

Frame alignment also allocates stack memory that needs to be accounted for.
Using the getMaxAlign() function added for this purpose.
seg-stacks: now crashing if no red zone is not specified

We want to crash if no red zone is not specified as the red zones concept
doesn't mix with seg stacks. Not diabling red zones could make the compiler do
dangerous assumptions about the stack.