Fix about 50 errors and many warnings without change process_64.o

arch/x86/kernel/process_64.o:
text    data     bss     dec     hex filename
5236       8      24    5268    1494 process_64.o.after
5236       8      24    5268    1494 process_64.o.before
md5:
9c35e9debdea4e471288c6e8ca267a75  process_64.o.after
9c35e9debdea4e471288c6e8ca267a75  process_64.o.before
Signed-off-by: Gustavo F. Padovan <gustavo@las.ic.unicamp.br>
Signed-off-by: Ingo Molnar <mingo@elte.hu>