Debug info: Use DW_OP_bit_piece instead of DW_OP_piece in the

Debug info: Use DW_OP_bit_piece instead of DW_OP_piece in the
intermediate representation. This
- increases consistency by using the same granularity everywhere
- allows for pieces < 1 byte
- DW_OP_piece didn't actually allow storing an offset.

Part of PR22495.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228631 91177308-0d34-0410-b5e6-96231b3b80d8