[Compiler] Add object ref discovery

Previously, the compiler ran a type inference pass to identify floating
point uses for register allocation.  The grand plan involves moving
all type inference into the Art compiler driver (using the results from
verification).  As a short-term workaround, this CL adds object reference
discovery to the type inference pass.  This is needed for LLVM-IR generation.

Change-Id: I655806264181bfd26ab9340582a02c657cd3f678
diff --git a/src/compiler/CompilerIR.h b/src/compiler/CompilerIR.h
index 2e0f6d5..972bfac 100644
--- a/src/compiler/CompilerIR.h
+++ b/src/compiler/CompilerIR.h
@@ -64,6 +64,7 @@
   unsigned defined:1;   // Do we know the type?
   unsigned fp:1;        // Floating point?
   unsigned core:1;      // Non-floating point?
+  unsigned ref:1;       // Something GC cares about
   unsigned highWord:1;  // High word of pair?
   unsigned home:1;      // Does this represent the home location?
   u1 lowReg;            // First physical register