Fix bug in PE/COFF plugin and ValueObjectVariable.

There are two bugs here.  The first is that MSVC and clang-cl
emit their bss section under the name '.data' instead of '.bss'
but with the size and file offset set to 0.  ObjectFilePECOFF
didn't handle this, and would only recognize a section as bss
if it was actually called '.bss'.  The effect of this is that
if we tried to print the value of a variable that lived in BSS
we would fail.

The second bug is that ValueObjectVariable was only returning
the forward type, which is insufficient to print the value of an
enum.  So we bump this up to the layout type.

Differential Revision: https://reviews.llvm.org/D54241

llvm-svn: 346430