amd64: Prevent initial IncSP from disappearing in corner cases.
amd64: Prevent initial IncSP from disappearing in corner cases.

This is the same correction as for ia32.
First construct all epilogues, then the prologue.
Check there, whether the IncSP has no users and add a keep edge in that case.

libfirm/libfirm,davidgiven/libfirm,killbug2004/libfirm,killbug2004/libfirm,killbug2004/libfirm,MatzeB/libfirm,davidgiven/libfirm,MatzeB/libfirm,jonashaag/libfirm,davidgiven/libfirm,jonashaag/libfirm,davidgiven/libfirm,MatzeB/libfirm,jonashaag/libfirm,MatzeB/libfirm,killbug2004/libfirm,8l/libfirm,MatzeB/libfirm,killbug2004/libfirm,jonashaag/libfirm,8l/libfirm,MatzeB/libfirm,davidgiven/libfirm,8l/libfirm,davidgiven/libfirm,libfirm/libfirm,8l/libfirm,killbug2004/libfirm,libfirm/libfirm,killbug2004/libfirm,8l/libfirm,jonashaag/libfirm,MatzeB/libfirm,jonashaag/libfirm,davidgiven/libfirm,libfirm/libfirm,8l/libfirm,8l/libfirm,libfirm/libfirm,jonashaag/libfirm