Implement MakeClosure
Implement MakeSlice
Various cleanups

Started working on interface ("invoke")
calls, not quite working yet though.
Merge branch 'ssa' of https://github.com/axw/llgo into ssa
Remove dead code
Implement append, work towards interfaces, panic/defer/recover

Lots of changes afoot to make interfaces work properly.
Unsure of how panic/defer/recover will work just yet;
may take this opportunity to move to using sjlj.
Numerous fixes

- Get rid of pointer, stack, method from LLVMValue;
  we always load when ssa tells us to deref, and we
  (should) never need to take the address of a var
  outside of ssa. There's a problem with *ssa.Index
  operating on array, instead of *array, though.
- Temporary (a sign I may be doing something wrong)
  hack to load arrays to stack when indexing.
- Move makeslice to runtime.
- Create globals with the right type.
- Always create blocks before use (ordering problem
  in defineFunction).
- "Backpatch" (to borrow a term used by adonovan)
  values not yet introduced to fr.env: create a
  placeholder (non-const!), and replace all uses
  when visiting the instruction that would define it.
- Temporarily make "panic()" a no-op.
Add interface receiver to type string
More fixes

- Create placeholder value (for backpatch) into its own
  basic block, so we can dispose of the instruction after
  replacing it.
- Remove receiver from interface method when invoking
  (it is implicit in the context pointer).
- Another fix for the Panic standin so we don't have missing
  terminators: call llvm.trap, emit unreachable.
Even more fixes!

- Build closures correctly (input is raw
  function pointer, not pair of pointers).
- Reimplement interface comparisons.

llgo-build runtime *almost* completes now.
I think it's just missing attribute processing,
to set global/function LLVM attributes.
Reenable source annotations

runtime is still not quite there.
Check if function exists before adding

Now I remember...
Moar fixes

- Check if function exists before adding in RuntimeFunction
- Don't use Create*Malloc builder functions; call the runtime.