Fix ptexViewer build with GLFW 2.x
Fix ptexViewer build with GLFW 2.x

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