Fix compilation error with CLEW enabled
Fix compilation error with CLEW enabled

For some reason it compiled fine on the desktop but
compilation on laptop requires explicit linking against
dl library.

shengfuintel/OpenSubdiv,poljere/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,xldeveloper/OpenSubdiv,takahito-tejima/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,jcowles/OpenSubdiv,nyotis/OpenSubdiv,lookup1980/OpenSubdiv,nyotis/OpenSubdiv,c64kernal/OpenSubdiv,shengfuintel/OpenSubdiv,lookup1980/OpenSubdiv,xldeveloper/OpenSubdiv,takahito-tejima/OpenSubdiv,jcowles/OpenSubdiv,jcowles/OpenSubdiv,poljere/OpenSubdiv,xldeveloper/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,nyotis/OpenSubdiv,anshuarya/OpenSubdiv,takahito-tejima/OpenSubdiv,c64kernal/OpenSubdiv,lookup1980/OpenSubdiv,anshuarya/OpenSubdiv,shengfuintel/OpenSubdiv,c64kernal/OpenSubdiv,poljere/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,anshuarya/OpenSubdiv