[DebugInfo] Add DW_AT_byte_size to vectors

Summary:
This patch adds the DW_AT_byte_size dwarf attribute to vectors.
This fixes PR21924

LLVM will round a vector up to the next alignable address, which can result in
the vector's representation in the object file being larger than what the
debugger will calculate via NumberOfElements * ElementSize. In such a case calling sizeof(MyVec) in the source will result in a different value than what a debugger might present. This situation can occur because LLVM permits non-power of two 'vector_size' attributes.

Reviewers: echristo, dexonsmith, aprantl

Reviewed By: aprantl

Subscribers: probinson, aprantl, llvm-commits, JDevlieghere

Tags: #debug-info

Differential Revision: https://reviews.llvm.org/D44048

llvm-svn: 327072