Extended Description

I've spun this off from bug 36322 to track additional issues with
the current implementation of DWARF descriptions of C99 VLAs.

Initially I was curious what happened if a function with a VLA was
inlined into another function. Adrian Prantl pointed out the test
llvm/test/DebugInfo/X86/vla-dependencies.ll
which I started playing with.

Even without optimization, some curious things happen.
The subrange_type has a DW_AT_type which points to something called
"sizetype" which does not exist in the source. It also doesn't share
an abbrev with the other base types, because its attributes are in a
different order; this suggests some poor internal coding practice at least,
although it's not actually invalid DWARF.

With optimization, LLVM asserts, which is worth its own bug.