[OpenCL] Fix for integer parameters of enqueue_kernel

Make handling integer parameters more flexible:

- For the number of events argument allow to pass larger
integers than 32 bits as soon as compiler can prove that
the range fits in 32 bits. If not, the diagnostic will be given.

- Change type of the arguments specifying the sizes of
the corresponding block arguments to be size_t.

Review: https://reviews.llvm.org/D26509
llvm-svn: 286849