Invoke support for Quick Compiler

Fleshed out invoke and const-string support.  Fixed a bug in Phi node
insertion.

With this CL, the "Recursive Fibonacci" and "HelloWorld" milestones are
met.

Added are a set of "HL" (for High-Level) invoke intrinsics.  Until we
complete the merging of the Quick & Iceland runtime models the invoke
code sequences are slightly different.  Thus, the Greenland IR needs
to represent invokes at a somewhat higher level than Iceland.  The
test for fast/slow path needs to happen during the lowering of the
HLInvokeXXX intrinsics in both the Quick and Portable paths.

This will generally be the case in the short term - push fast/slow
path determination below the Greenland IR level.  As unification
proceeds, we'll pull as much as makes sense into the common front end.

Change-Id: I0a18edf1be18583c0afdc3f7e10a3e4691968e77