fix msvc configure

visual studio targets do not depend on executables, only the projects
produced.
tested with --target=x86-win32-vs9
fixes:
...
make[1]: *** No rule to make target `test_libvpx', needed by `.bins'.
Stop.
Makefile:17: recipe for target `.DEFAULT' failed

Change-Id: I606ab32d5e26fee352f25c822e0f496eff165382
1 file changed