matlab mex cannot find vcomp.lib when openmp is used

I am trying to mex a c++ source file containing openmp usages. In the mex command, i have added COMPFLAGS="/openmp $COMPFLAGS" but it says cannot find vcomp.lib. My matlab mex have been setup to use the compiler of Windows SDK 7.1 located in C:\Program Files. I checked the lib files inside this SDK and didn't find vcomp.lib. Anyone knows how can I install openmp to Windows SDK 7.1? Thanks a lot!