I received this patch from Jeff Law as a fix for build failures with the
upcoming GCC 9. The following is Jeff Law's description of the patch:

 Attached you'll find the fix for criu.  You'll see it's just a matter
 of dropping the sp/esp clobber from the relevant asm statements.  THe
 details:

 criu has a macro which defines an asm which appears to want to set a new
 stack pointer, then directly issue a sigreturn call to the kernel.  Some
 variants clobber sp (aarch64, arm, x86), others do not (ppc, s390)

 While the asm does indeed set a new stack pointer, we never return from
 a sigreturn syscall -- at least not in the normal way.  We actually
 return back to the point where the process was interrupted by the
 signal.  So describing the affect of the asm on the stack pointer is
 pedantically correct, it actually has no real effect and can just be
 dropped to avoid the hard error from gcc-9.
Suggested-by: Jeff Law <law@redhat.com>
Reviewed-by: Dmitry Safonov <0x7f454c46@gmail.com>
Signed-off-by: Adrian Reber <areber@redhat.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>