ARC: ported the GC tests over to --gc:arc

lib/core/runtime_v2.nim

@@ -135,6 +135,18 @@ proc GC_ref*[T](x: ref T) =
   ## New runtime only supports this operation for 'ref T'.
   if x != nil: nimIncRef(cast[pointer](x))
 
+template GC_fullCollect* =
+  ## Forces a full garbage collection pass. With ``--gc:arc`` a nop.
+  discard
+
+template setupForeignThreadGc* =
+  ## With ``--gc:arc`` a nop.
+  discard
+
+template tearDownForeignThreadGc* =
+  ## With ``--gc:arc`` a nop.
+  discard
+
 proc isObj(obj: PNimType, subclass: cstring): bool {.compilerRtl, inl.} =
   proc strstr(s, sub: cstring): cstring {.header: "<string.h>", importc.}