AC_OBJEXT again

[Lars J. Aas]

When the w32 free Borland C++ command line compiler links a program
(conftest.exe), it also produces a file named `conftest.tds' in
addition to `conftest.obj'.  In AC_OBJEXT, conftest.* is globbed to
`... conftest.obj conftest.tds', and the for loop ends up deciding
that $ac_objext should be `tds'.

One possible fix is to put `*.tds' in as an exception in the for loop.
A better one is probably to do a prioritized search on *.o *.obj with
a fallback on the conftest.* glob approach...

  Lars J