[PATCH] style fix for aix51.h and rs6000/mach.h

[David Edelsohn]

	aix51.h is nearly identical to aix43.h except for a few tweaks.
aix51.h definitely does not need the double inclusion.  I do not see many
#undefs which differ between the two.

	Some of the WCHAR macros probably would be more appropriate in
aix.h than in rs6000.h, but would need to be #undefed anyway.  If one
wants to avoid #undef, one needs another layer of aix4.h and aix5.h.

David