Minor tweaks to integration of assembler part.

Remove unneeded PC restore in vm_growstack_*.
Don't declare symbols that are unused in interpreter-only builds.
Don't embed lj_vm_foldfpm in interpreter-only builds.
Add 2nd temporary TValue in lua_State.

src/lj_obj.h

@@ -480,7 +480,7 @@ typedef struct global_State {
   uint8_t vmevmask;	/* VM event mask. */
   GCRef mainthref;	/* Link to main thread. */
   TValue registrytv;	/* Anchor for registry. */
-  TValue tmptv;		/* Temporary TValue. */
+  TValue tmptv, tmptv2;	/* Temporary TValues. */
   GCupval uvhead;	/* Head of double-linked list of all open upvalues. */
   int32_t hookcount;	/* Instruction hook countdown. */
   int32_t hookcstart;	/* Start count for instruction hook counter. */