When opencl-clang is used in-tree of a project, these two variables may
be defined in CMakeLists.txt of the project. This PR makes the variable
names clear that they are intended for opencl-clang library and easily
distinguishable from other variables in CMakeLists.txt of the project.
When opencl-clang is used in-tree of a project, these two variables may be defined in CMakeLists.txt of the project. This PR makes the variable names clear that they are intended for opencl-clang library and easily distinguishable from other variables in CMakeLists.txt of the project.