Use MCFillFragment for zero-initialized data.
It fixes PR16338 (ICE when compiling very large two-dimensional array).

Differential Revision: http://llvm-reviews.chandlerc.com/D1043


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185080 91177308-0d34-0410-b5e6-96231b3b80d8