[Windows] Remove functions in intrin.h that are defined in Builtin.def.

Summary:
These duplicate declarations cause a problem for CUDA compiles on
Windows.  All implicitly-defined functions are host+device, and this
applies to the declarations in Builtin.def.  But then when we see the
declarations in intrin.h, they have no attributes, so are host-only
functions.  This is an error.

(A better fix might be to make these builtins host-only, but that is a
much bigger change.)

Reviewers: rnk

Subscribers: cfe-commits, echristo

Differential Revision: https://reviews.llvm.org/D28317

llvm-svn: 291128