gdb/dwarf: factor out to cutu_reader::skip_one_attribute method

I was reading cutu_reader::skip_one_die, and thought that the code to
skip one attribute made it quite difficult to read.  Factor this code
out to a new method, to get it out of the way.

As a bonus, it transforms one goto in a recursion call, which is also
easier to follow.  Unfortunately, I have no idea how to test
DW_FORM_indirect, as it doesn't seem to appear anywhere in the
testsuite, and I don't think that compilers often emit that.

Change-Id: I2257b3e594aafb7c7da52ddd55baa651cefb802f
Approved-By: Tom Tromey <tom@tromey.com>
2 files changed