x86_64: ia32_signal.c: use macro instead of immediate

Make and use macro FIX_EFLAGS, instead of immediate value 0x40DD5 in
ia32_restore_sigcontext().

Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Acked-by: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>