Use uint64_t for GoArray size.

Summary:
This was int64_t, but all usages of it came from code that was passing
in unsigned values. The usages of the array size, except for one, were
also treating it as an unsigned value.  The usage that treated it as
signed was to try to figure out if it was a complete type or not, but
the callers creating the array didn't seem to be aware of using -1 as
an indicator for an incomplete array.

Reviewers: ribrdb, clayborg

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D12872

llvm-svn: 247662