x/debug: handle some more cases for struct member offset encoding in the DWARF parser.

These cases were used in older compiler versions.  We also check that we
consumed all the opcodes in the buffer, otherwise we probably didn't
interpret it correctly.

Change-Id: If918dbdcb824a5d4e5add1c9333b34aae9d6d0b4
Reviewed-on: https://go-review.googlesource.com/19212
Reviewed-by: Dave Day <djd@golang.org>
2 files changed