Bug 7458: Implement primitive-mep-apply-with-optionals

* sources/dfmc/llvm-back-end/llvm-primitives-lambda.dylan
  (primitive primitive-mep-apply-with-optionals): Fill in implementation.
Bug 7458: Update Mac OS target strings

* sources/dfmc/llvm-back-end/llvm-targets.dylan
  (llvm-back-end-target-triple on <llvm-x86-darwin-back-end>):
   Update to "i386-apple-macosx10.7.0" (supporting Mac OS Lion and later).
  (llvm-back-end-data-layout on <llvm-x86-darwin-back-end>): Update to match
   clang target layout.
  (llvm-back-end-target-triple on <llvm-x86_64-darwin-back-end>):
   Update to "x86_64-apple-macosx10.7.0" (supporting Mac OS Lion and later).
  (llvm-back-end-data-layout on <llvm-x86_64-darwin-back-end>): Update to match
   clang target layout.
dfmc-debug-back-end: Distinguish <method-apply> for printing

Distinguish <method-apply> computations from <apply> in printed DFM
output.

* sources/dfmc/debug-back-end/print-flow-graph.dylan
  (operation-name on <method-apply>): New method.
Bug 7458: Allow changing section names for thread-local data

* sources/dfmc/llvm-back-end/llvm-sections.dylan
  (llvm-section-name): Add a thread-local? keyword. Use null section names
   for thread-local #"variables" and #"untraced-data".

* sources/dfmc/llvm-linker/llvm-link-object.dylan
  (emit-definition on <module-binding>): Pass thread-local? keyword to
   llvm-section-name.

* sources/dfmc/llvm-back-end/llvm-primitives.dylan
  (llvm-runtime-variable): Pass thread-local? keyword to
   llvm-section-name.
Work-in-progress snapshot