[OpenCL] Traverse vector types for ocl extensions support

Summary:
Given the following kernel:
__kernel void foo() {
  double d;
  double4 dd;
}

and cl_khr_fp64 is disabled, the compilation would fail due to
the presence of 'double d', but when removed, it passes.

The expectation is that extended vector types of unsupported types
will also be unsupported.

The patch adds the check for this scenario.

Patch by: Ofir Cohen

Reviewers: bader, Anastasia, AlexeySotkin, yaxunl

Reviewed By: Anastasia

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D51296

llvm-svn: 341309