add initial openmp support for matrix-matrix products => x1.9 speedup on my core2 duo
add initial openmp support for matrix-matrix products
=> x1.9 speedup on my core2 duo

ritsu1228/eigen,toastedcrumpets/eigen,pasuka/eigen,TSC21/Eigen,ROCmSoftwarePlatform/hipeigen,pasuka/eigen,Zefz/eigen,ritsu1228/eigen,Zefz/eigen,ROCmSoftwarePlatform/hipeigen,ritsu1228/eigen,pasuka/eigen,ROCmSoftwarePlatform/hipeigen,Zefz/eigen,TSC21/Eigen,ritsu1228/eigen,TSC21/Eigen,Zefz/eigen,ritsu1228/eigen,TSC21/Eigen,pasuka/eigen,toastedcrumpets/eigen,ROCmSoftwarePlatform/hipeigen,pasuka/eigen,toastedcrumpets/eigen,toastedcrumpets/eigen