x86: boot/compressed/vmlinux.lds.S: fix build of bzImage with 64 bit compiler

Jesper reported that he saw following build issue:

 > ld:arch/x86/boot/compressed/vmlinux.lds:9: syntax error
 > make[2]: *** [arch/x86/boot/compressed/vmlinux] Error 1
 > make[1]: *** [arch/x86/boot/compressed/vmlinux] Error 2
 > make: *** [bzImage] Error 2

CPP defines the symbol "i386" to "1".
Undefine this to fix it.

[ Impact: build fix with certain tool chains ]
Reported-by: Jesper Dangaard Brouer <jdb@comx.dk>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <alpine.LFD.2.00.0904260958190.3101@localhost.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/boot/compressed/vmlinux.lds.S

 OUTPUT_FORMAT(CONFIG_OUTPUT_FORMAT, CONFIG_OUTPUT_FORMAT, CONFIG_OUTPUT_FORMAT)
 
+#undef i386
+
 #ifdef CONFIG_X86_64
 OUTPUT_ARCH(i386:x86-64)
 ENTRY(startup_64)