bugfix: tcan_inherit_generic works again

compiler/types.nim

@@ -92,7 +92,7 @@ proc InvalidGenericInst(f: PType): bool =
 
 proc isPureObject(typ: PType): bool = 
   var t = typ
-  while t.sons[0] != nil: t = t.sons[0]
+  while t.kind == tyObject and t.sons[0] != nil: t = t.sons[0]
   result = t.sym != nil and sfPure in t.sym.flags
 
 proc getOrdValue(n: PNode): biggestInt = 

tests/compile/tmacroaspragma.nim

@@ -0,0 +1,8 @@
+import macros
+
+macro foo(x: stmt): stmt =
+  echo treerepr(callsite())
+  result = newNimNode(nnkStmtList)
+
+proc zoo() {.foo.} = echo "hi"
+