When GCC went from version 8 to version 9, it started inserted endbr64 instructions into
the generated .s code.  endbr64 is a signal that the address is a valid target for an indirect
jump.  Code thus annotated is more resistant to hacking and errors.  But it messes up our ability
to trick GDB into showing us good line numbers when stepping into subroutines, so I modified
SFIX to just strip them out.