fix #16752: threadvar now works with importcpp types; osx now uses native TLS (--tlsEmulation:off), which can be orders of magnitude faster (#16750)

* osx now uses native TLS, which can be orders of magnitude faster

* add {.cppNonPod.}

* improve test

* changelog, docs, disable part of windows test

compiler/options.nim

@@ -380,11 +380,12 @@ proc hasWarn*(conf: ConfigRef, note: TNoteKind): bool =
 
 proc hcrOn*(conf: ConfigRef): bool = return optHotCodeReloading in conf.globalOptions
 
-template depConfigFields*(fn) {.dirty.} =
-  fn(target)
-  fn(options)
-  fn(globalOptions)
-  fn(selectedGC)
+when false:
+  template depConfigFields*(fn) {.dirty.} = # deadcode
+    fn(target)
+    fn(options)
+    fn(globalOptions)
+    fn(selectedGC)
 
 const oldExperimentalFeatures* = {implicitDeref, dotOperators, callOperator, parallel}