Improved DWARFv4 support.

Improved DWARFv4 support.

Handle DW_AT_data_member_location attributes with type DW_FORM_data*, which
store a simple integer offset rather than dwarf expression. This seems to come
up with struct members, at least on ARM.

Handle DW_AT_location attributes with type DW_FORM_sec_offset as not having
dwarf expressions, as allowed by the DWARFv4 standard. This seems to come up
with some local variables, at least on ARM.

Test DW_FORM_sec_offset support in location lists and DW_AT_data_member_location formatting support.
Test code, compiled with gcc (Ubuntu 4.8.4-2ubuntu1~14.04) 4.8.4 on x86-64:

struct Foo {
  char bim : 8;
  char bar : 3;
  char baz : 5;
};

int get_bar(struct Foo foo) {
  return foo.bar;
}

int f1(int a, char b) {
  return a+b;
}