[SWIFTSHADER] building from clvk root cmake is broken

[rjodinchr]

Trying to build swiftshader from clvk cmake does not work anymore. It seems that swiftshader is trying to use a mix of LLVM from its own third_party dependencies and the one for clvk. But there are not at the same version (10 vs ToT), which make swiftshader build fail.

Workaound: build swiftshader on its own as it is done in azur