DebugInfo: Use DW_FORM_data4 for DW_AT_high_pc in DW_TAG_lexical_blocks

Suggested by Adrian Prantl in code review for r203187

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203323 91177308-0d34-0410-b5e6-96231b3b80d8