Avoid conflicing redefinitions of strupr() & strrev()

[th-otto]

No description provided.

[OmniBlade]

#820 would resolve this by detecting these and other platform specific functions at configure time so no need for platform specifics, but needs reviewing and merging.

[th-otto]

Yes, i agree, there are certainly better ways to fix this, my approach was just to fix compilation on MiNT (it complains because it was already declared in <string.h> and then declared static in wwstd.h), without breaking other platforms.

Another simple solution might be to just use different name, like is done with _strlwr.