Bug 7440: Add support for LLVM module flags

* sources/lib/llvm/llvm-module.dylan
  (llvm-module-add-flag): New function for adding module flags via the
  !llvm.module.flags named metadata item.

* sources/lib/llvm/llvm-library.dylan
  (module llvm): Export llvm-module-add-flag.
Bug 7440: Mark debug metadata for LLVM tools

* sources/lib/llvm/llvm-debug.dylan
  ($llvm-debug-metadata-version): New constant.
  (llvm-make-dbg-compile-unit): When debug information is used, mark
   the module using the "Debug Info Version" module flag.
Bug 7440: Improve error handling for ins--gep

* sources/lib/llvm/llvm-builder.dylan
  (ins--gep): Force the value type of getelementptr instructions
   to be computed as they are built rather than delaying type
   errors to bitcode emission time.
Bug 7458: Emit typedef debug-info for <object> references

* sources/dfmc/llvm-back-end/llvm-emit-debug.dylan
  (llvm-reference-dbg-type): Use a typedef (dylan_value) within the
   definition of the debug type of general <object> references.
Bug 7440 7458: Update debug info generation for LLVM 3.5

* sources/lib/llvm/llvm-debug.dylan
  (llvm-make-dbg-compile-unit): Add a kind: keyword describing the
   type of debug info. Update "Debug Info Version" module flag, and
   add a "Dwarf Version" module flag.
  (llvm-make-dbg-function-type): Correct debug info generation.
  (llvm-make-dbg-function): Correct debug info generation
  (llvm-make-dbg-lexical-block): Add discriminiator: keyword and
   add the discriminator value to the debug info.
  (llvm-make-dbg-unspecified-parameters): New function for generating
   the marker used with varargs functions.

* sources/lib/llvm/llvm-library.dylan
  (module llvm-debug): Export llvm-make-dbg-unspecified-parameters.

* sources/dfmc/llvm-back-end/llvm-emit-debug.dylan
  (llvm-reference-dbg-type on <&raw-struct-type>): Include dummy dbg-file
   information.
  (llvm-reference-dbg-type on <&type>): Include dummy dbg-file
   information.
Bug 7440: Allow generating assembly language debug info

* sources/lib/llvm/llvm-debug.dylan
  ($DW-LANG-Mips-Assembler): Define user-area constant traditionally
   used for adding assembly-language debug info.
  (module llvm-debug): Export $DW-LANG-Mips-Assembler.