Updated the windows build system to link the user given openmp
library using -DOpenMP_libomp_LIBRARY=<Desired lib name> option
using command line or through cmake-gui application to build
blis library and its test applications. If user not given any
openmp library then by default openmp library will be
C:/Program Files/LLVM/lib/libomp.lib.
Change-Id: I07542c79454496f88e65e26327ad76a7f49c7a8c