Cmake/deps: Update OSL to 1.11.10.0

This bumps OSL to 1.11.10.0. OSL Has a new build time
dependency: Clang, and more importantly it expects
clang and llvm to share a library folder, which it
previously for us did not.

This patch changes:

-OSL Update to 1.11.10.0

-refactor the llvm/clang/clang-tools-extra builds into the llvm
 build using the llvm-project tarball for building that has all
 of the subprojects in it.

-update ispc/openmp builds since clang no longer its own dependency
 and they have to depend on the llvm build now.

-Update the windows builder to use the 64 bit host tools since it
 ran out of ram linking clang

-Since OSL now needs clang to link successfully a findclang.cmake
 has been provided for linux/OSX

Differential Revision: https://developer.blender.org/D10212

Reviewed By: brecht, sebbas, sybren