On Mac, don't use glDraw*BaseInstance because it's not available.
Clean up some code that was producing warnings in sb6ktx.cpp.
Add error logging to stderr when shader compilation fails in sb6shader.cpp.
Locally remove definition of GLhandleARB form glcorearb.h as we're not
using it and it's conflicting with system headers on Mac.
Drop shader version in alienrain sample to 410 to cater for Mac.
Drop shader version in basicfbo sample to 410 for Mac.
Drop shader version in blendmatrix sample down to 410 for Mac.
Drop shader version in gsculling.cpp to 410 for Mac build. This sample
doesn't work yet. Still needs to be debugged.
Drop shader version to 410 for wrapmodes sample for Mac build.
Drop shader version to 410 for gstessellate example.
Drop shader version for instancedattribs example down to 410 for Mac build.
Drop shader version of starfield example to 410 for Mac build.
Drop shader version in spinnycube example to 410 for Mac build.
Drop shader version in linesmooth example to 410 for Mac build.
Drop shader version of normalviewer to 410 for Mac build.
Drop shader version of objectexploder example down to 410 for Mac version.
Drop shader version in shadedpoints example to 410 for Mac.
Drop shader version of noperspective example to 410 and fix shader
body for lower version for Mac.
Drop shader version for polygonsmooth example to 410 for Mac.
Minor fixes to perf-readpixels.cpp to get compiling on Mac.
Drop movingtri shader version to 410 for Mac.