Cycles / OSL: Updare stdosl.h to 1.7.1
Cycles / OSL: Updare stdosl.h to 1.7.1

This updates our file to OSL 1.7.1, which comes with some new inbuilt
features:

- linearstep()
- smooth_linearstep()

- hash()
- getchar()

tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird