x86_64-xlate.pl commentary section update.

# arguments passed to callee, *but* not less than 4! This means that

# upon function entry point 5th argument resides at 40(%rsp), as well

# as that 32 bytes from 8(%rsp) can always be used as temporal

# storage [without allocating a frame].

# storage [without allocating a frame]. One can actually argue that

# one can assume a "red zone" above stack pointer under Win64 as well.

# Point is that at apparently no accasion Windows would alter the area

# above stack pointer in true asynchronous manner...

#

# All the above means that if assembler programmer adheres to Unix

# register and stack layout, but disregards the "red zone" existense,