[clang] Handle __declspec() attributes in using

This patch fixes so that declspec attributes are forwarded
to the alias declaration.

Before this patch this would assert:

class Test { int a; };
using AlignedTest = __declspec(align(16)) const Test;
static_assert(alignof(AlignedTest) == 16, "error");

But afterwards it behaves the same as MSVC does and doesn't
assert.

Fixes: llvm/llvm-project#60513

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D143632