[debug-early] handle objects containing variable-length members

[Aldy Hernandez <aldyh at redhat dot com>]

The attached patch handles late dwarf annotations to objects containing 
variable-length members.  It fixes the following regressions in the gdb 
testsuite:

> FAIL: gdb.base/vla-datatypes.exp: print vla_struct_object
> FAIL: gdb.base/vla-datatypes.exp: print vla_union_object
> FAIL: gdb.base/vla-datatypes.exp: ptype vla_struct_object
> FAIL: gdb.base/vla-datatypes.exp: ptype vla_union_object
> FAIL: gdb.base/vla-datatypes.exp: size of vla_struct_object
> FAIL: gdb.base/vla-datatypes.exp: size of vla_union_object

I am not convinced this is the last patch to variable-length variables, 
so it may require further refining, but it does get us down to ZERO gdb 
regressions which is A Good Thing (TM).

The only differences I see for trunk and the debug-early branch wrt gdb 
regressions are:

< KFAIL: gdb.cp/oranking.exp: p foo4(&a) (PRMS: gdb/12098)
---
> KPASS: gdb.cp/oranking.exp: p foo4(&a) (PRMS gdb/12098)
20065c20065
< KFAIL: gdb.cp/oranking.exp: p foo101("abc") (PRMS: gdb/12098)
---
> KPASS: gdb.cp/oranking.exp: p foo101("abc") (PRMS gdb/12098)
28222c28222

Plus some noise regarding threads.

I don't know what KFAIL/KPASS are, having lived in GCC land too long, 
but I will take a look at those next.

Committed to branch.
Aldy

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