[tlbuild] Fail to set macros in c-auto.h for MinGW -- if not build in source tree

[Karl Berry]

Hi again,

     And I would suggest to change two lines in 'status.m4'  from

You need to be the one to take the changes up with the autoconf
maintainers.  I can't be the one to argue for mingw changes.  And we
don't want to change core autoconf macros in our tree, that would not be
a good approach.

Anyway, glad you finally got it going.

Best,
karl