fix #10339 by returning type attached to nkEmpty (#10370)

* fix #10339 by checking for nkObjConstr

* revert check for nkObjConstr, return type from nkEmpty node

The correct type needed in `semObjConstr` to fix #10339 is indeed
available, but attached to an `nkEmpty` node. These were previously
discarded in `semTypeNode`, which is used to extract the type for the
object.

* simplify return of PType from  `nkEmpty`

* also fixes #9866, add test case

tests/statictypes/tstatictypes.nim

@@ -137,3 +137,20 @@ block:
   type
     Coord[N: static[int]] = tuple[col, row: range[0'i8 .. (N.int8-1)]]
     Point[N: static[int]] = range[0'i16 .. N.int16 * N.int16 - 1]
+
+# https://github.com/nim-lang/Nim/issues/10339
+block:
+  type
+    MicroKernel = object
+      a: float
+      b: int
+
+  macro extractA(ukernel: static MicroKernel): untyped =
+    result = newLit ukernel.a
+
+  proc tFunc[ukernel: static MicroKernel]() =
+    const x = ukernel.extractA
+    doAssert x == 5.5
+
+  const uk = MicroKernel(a: 5.5, b: 1)
+  tFunc[uk]()