[CMake] target name tweak

[SK]

When using the D language compiler 'dmd' on windows, I'm stuck with a
linker that gets confused with object file names like foo.c.obj.  The
linker can only handle a single dot in the object file name, as in
foo.o

How can I set target names to just be the base name without the source
extension?  I need to do this in the language support module, e.g.
Modules\Platform\Windows-dmd.cmake, so that users don't need to hack
this in their own CMakeLists.txt files.

Thanks for any help!
-steve