Support memory intrinsics

  This patch adds support for memcpy, memset and memmove intrinsics. They are
  represented as one (memset) or two (memcpy, memmove) memory accesses in the
  polyhedral model. These accesses have an access range that describes the
  summarized effect of the intrinsic, i.e.,
    memset(&A[i], '$', N);
  is represented as a write access from A[i] to A[i+N].

Differential Revision: http://reviews.llvm.org/D5226

llvm-svn: 261489