DebugInfo: change alignment type from uint64_t to uint32_t to save space.

DebugInfo: change alignment type from uint64_t to uint32_t to save space.
In futher patches we shall have alignment field added to DIVariable family
and switching from uint64_t to uint32_t will save 4 bytes per variable.

Differential Revision: https://reviews.llvm.org/D25620

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284482 91177308-0d34-0410-b5e6-96231b3b80d8