x86: Fix compile error with CONFIG_AS_CFI=n

   AS      arch/x86/lib/csum-copy_64.o
arch/x86/lib/csum-copy_64.S: Assembler messages:
arch/x86/lib/csum-copy_64.S:48: Error: Macro `ignore' was already defined
make[1]: *** [arch/x86/lib/csum-copy_64.o] Error 1
make: *** [arch/x86/lib] Error 2

It appears that csum-copy_64.S and dwarf2.h both define an ignore macro. 
I would expect one of them can be renamed quite easily, unless they 
are references elsewhere. 

Caused-by-commit: 392a0fc9


    x86: merge dwarf2 headers

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>