Check if First argument in _builtin_assume_aligned_ is of pointer type

Currently clang doesn't verify if the first argument in
`_builtin_assume_aligned` is of pointer type. This leads to an
assertion build failure. This patch aims to add a check if the first
argument is of pointer type or not and diagnose it with
diag::err_typecheck_convert_incompatible if its not of pointer type.

Fixes https://github.com/llvm/llvm-project/issues/62305
Differential Revision: https://reviews.llvm.org/D149514