hwasan: Align n_namesz and n_descsz to 4 when reading notes.

There is no requirement for the producer of a note to include the note
alignment in these fields. As a result we can end up missing the HWASAN note
if one of the other notes in the binary has the alignment missing.

Differential Revision: https://reviews.llvm.org/D66692

llvm-svn: 369826