[OpenCL] Prevent mangling kernel functions.

Authored by Anastasia on May 7 2019, 7:22 AM.


[OpenCL] Prevent mangling kernel functions.

Kernel function names have to be preserved as in the original
source to be able to access them from the host API side.

This commit also adds restriction to kernels that prevents them
from being used in overloading, templates, etc.

Differential Revision: https://reviews.llvm.org/D60454

llvm-svn: 360152