BUG: Avoid using def file when BUILD_SHARED_LIBS is off

Using the def file causes test failures after building with the
Visual Studio 11 linker, when building static libraries.

The net result was that the executables that linked to this build
would be looking for a vtktiff.dll even though there wasn't a dll
file. Somehow including the def file in the lib-building command
line caused the exports to be in the .lib file which made the
linked executable appear to depend on a corresponding dll file...
Very strange.

Since the def file is only for specifying exports in the shared
library build, it should be ok to leave it out for static library
builds.

Change-Id: I565c18014f28764188dee86db998e4b50f0d8024
Merge topic 'avoid-def-file-for-static-builds' into master

8c1893f8 BUG: Avoid using def file when BUILD_SHARED_LIBS is off