finding where a macro is redefined

[Trevis Rothwell]

GCC tells me that I am redefining a macro.  I have searched my code
several times, and no-where is this macro explicitly redefined.  I've
seen this sort of error before, with the culprit being a misplaced
brace character or some such thing.

Any suggestions for more speedily tracking this problem down?
Manually searching the code will likely turn it up, but there's a lot
to search through, and several hours later I haven't found it yet.

Thanks!