Initial support for JITting C-style for loops

Does not handle next/last/redo (and goto...).
Make last_op() work after JITting, when the unstack op has been detached
Replace generic pa_pp_op call with pa_pp_unstack
Replace generic pa_pp_op call with pa_pp_nextstate
Support for JITting while/until loops

Does not support do {} while/until loops (requires being able
to JIT blocks).
First skeleton implementation using LLVM as the generator
Static LLVM library build fix
Fix engine/module ownership

LLVM execution engine owns the module, which owns the functions, therefore the
JITted ops must own a (shared) execution engine.

Since there is no need of a separate Emit class, the features of the Emit class
have been moved to a per-interpreter structure. This should work reasonably
well with the move to MCJIT in LLVM 3.5.
Ditch more of the old prototype code
Automate the creation of emitters for snippets of C code

Currently used to create emitters for Perl API functions/macros.

It assembles the snippets in a C file, compiles it to LLVM bytecode with clang,
uses llc to generate the LLVM API calls corresponding to the bytecode and then
butchers the resulting source code into an emitter class.
More flexible LLVM version requirement

My silly build now claims "3.4svn". *sigh*
Perl::JIT+LLVM build fix: hide -g flag from clang

clang will puke if using -g trying to emit LLVM IR.
Silience very noisy and spurious warnings
Fix valid compiler warnings
Fix trivial test failure

Fix some trivial test failures so the test can
eventually become useful again.
Adjust ignorance to LLVM garbage