PR13337: Omit DW_TAG_restrict_type when compiling for DWARF2

DWARF3 introduced DW_TAG_restrict_type, so avoid using it in prior
versions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206105 91177308-0d34-0410-b5e6-96231b3b80d8