Fix non-determinism in order of LLVM attributes

We were using array_pod_sort on an array of type 'Attribute', which
wraps a pointer to AttributeImpl. For the most part this didn't matter
because the printing code prints enum attributes in a defined order, but
integer attributes such as 'align' and 'dereferenceable' were not
ordered.

Furthermore, AttributeImpl::operator< was broken for integer attributes.
An integer attribute is a kind and an integer value, and both pieces
need to be compared.

By fixing the comparison operator, we can go back to std::sort, and
things look good now.  This should fix clang arm-swiftcall.c test
failures on Windows.

llvm-svn: 265361