x86: early_idt_handler improvements, 64-bit

It's not too pretty, but I found this made the "PANIC: early exception"
messages become much more reliably useful: 1. print the vector number,
2. print the %cs value, 3. handle error-code-pushing vs non-pushing vectors.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/include/asm-x86/segment.h b/include/asm-x86/segment.h
index 57c8d37..23f0535 100644
--- a/include/asm-x86/segment.h
+++ b/include/asm-x86/segment.h
@@ -195,4 +195,10 @@
 #define GDT_ENTRY_TLS_ENTRIES 3
 #define TLS_SIZE (GDT_ENTRY_TLS_ENTRIES * 8)
 
+#ifdef __KERNEL__
+#ifndef __ASSEMBLY__
+extern const char early_idt_handlers[IDT_ENTRIES][10];
+#endif
+#endif
+
 #endif