macros: Introduce sameType(a, b) for node types

Previously introduced node comparison `==` was working somehow wrong on nodes
returned from getType(a), comparing just ids of the symbols.

Recently introduced `==` change 47dce26886
started comparing symbol nodes pointer-wise, thus strictly. Since getType(a)
always creates new symbol pointing to the type, comparing two such nodes using
`==` always returns false, even they point to the same type.

That is why we need a new sameType macro to be able to tell if these nodes
point to the same type.

compiler/vmgen.nim

@@ -991,6 +991,7 @@ proc genMagic(c: PCtx; n: PNode; dest: var TDest; m: TMagic) =
   of mIdentToStr: genUnaryABC(c, n, dest, opcIdentToStr)
   of mEqIdent: genBinaryABC(c, n, dest, opcEqIdent)
   of mEqNimrodNode: genBinaryABC(c, n, dest, opcEqNimrodNode)
+  of mSameNodeType: genBinaryABC(c, n, dest, opcSameNodeType)
   of mNLineInfo: genUnaryABC(c, n, dest, opcNLineInfo)
   of mNHint:
     unused(n, dest)