New feature: add support for target intrinsics being defined in the

New feature: add support for target intrinsics being defined in the
target directories themselves.  This also means that VMCore no longer
needs to know about every target's list of intrinsics.  Future work
will include converting the PowerPC target to this interface as an
example implementation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@63765 91177308-0d34-0410-b5e6-96231b3b80d8