Fix destructor injections for global variables (#11230)

* attach global destructors at end of mainModule
* Add testcase
* Minor cleanup
* Inject topLevelVar temporaries' destructors early
* Fix megatest

tests/destructor/objFile.nim

@@ -0,0 +1,8 @@
+type Obj* = object
+  v*: int
+
+proc `=destroy`(this: var Obj) =
+  echo "igotdestroyed"
+  this.v = -1
+
+var test* = Obj(v: 42)

tests/destructor/texplicit_move.nim

@@ -6,6 +6,7 @@ discard """
 10
 destroyed!
 '''
+joinable: false
 """
 
 type

tests/destructor/tglobaldestructor.nim

@@ -0,0 +1,9 @@
+discard """
+  cmd: '''nim c --newruntime $file'''
+  output: '''(v: 42)
+igotdestroyed'''
+"""
+
+import objFile
+
+echo test

tests/destructor/topt.nim

@@ -3,6 +3,7 @@ discard """
   output: '''5
 vseq destroy
 '''
+joinable: false
 """
 type
   opt*[T] = object