Port bones.gc math to GOAL (#3425)

Reverse engineer the skinning matrix calculation and port to GOAL. This
is about 3x faster than the MIPS2c version.

As usual, there is a `*use-new-bones*` flag to go back to the old
version.

Fix for a bug in the compiler's `.div.vf` implementation (only happens
if src/dst are the same), and fix for a typo in the register allocator
that would sometimes cause it not to consider xmm8-xmm15.

goalc/regalloc/allocator_interface.cpp

@@ -24,7 +24,7 @@ void print_allocate_input(const AllocationInput& in) {
     }
   } else {
     for (const auto& instruction : in.instructions) {
-      lg::print(" [{:3d}] {}\n", instruction.print());
+      lg::print(" {}\n", instruction.print());
     }
   }
   lg::print("[RegAlloc] Debug Input Constraints:\n");