Fix PR rtl-optimization/100411

Fix PR rtl-optimization/100411

This is the bootstrap failure of GCC 11 on MinGW64 configured with --enable-
tune=nocona.  The bottom line is that SEH does not support CFI for epilogues
but the x86 back-end nevertheless attaches it to instructions, so we have to
filter it out and this is done by detecting the end of the prologue by means
of the NOTE_INSN_PROLOGUE_END note.

But the compiler manages to generate a second epilogue before this note in
the RTL stream and this fools the aforementioned logic.  The root cause is
cross-jumping, which inserts a jump before the end of the prologue, in fact
just before the note; the rest (CFG cleanup, BB reordering, etc) is downhill
from there.

gcc/
	PR rtl-optimization/100411
	* cfgcleanup.c (try_crossjump_to_edge): Also skip end of prologue
	and beginning of function markers.