fixes #8671; show helpful msg (lookup symbol, eg iterator) on 'attempting to call undeclared routine' error (#8786)

tests/errmsgs/undeclared_routime.nim

@@ -0,0 +1,13 @@
+discard """
+cmd: '''nim c --hints:off $file'''
+errormsg: "attempting to call routine: 'myiter'"
+nimout: '''undeclared_routime.nim(13, 15) Error: attempting to call routine: 'myiter'
+  found 'undeclared_routime.myiter(a: string)[declared in undeclared_routime.nim(10, 9)]' of kind 'iterator'
+  found 'undeclared_routime.myiter()[declared in undeclared_routime.nim(11, 9)]' of kind 'iterator'
+'''
+"""
+
+iterator myiter(a:string): int = discard
+iterator myiter(): int = discard
+
+let a = myiter(1)

tests/errmsgs/undeclared_routime2.nim

@@ -0,0 +1,9 @@
+discard """
+cmd: '''nim c --hints:off $file'''
+errormsg: "invalid pragma: myPragma"
+"""
+
+proc myPragma():int=discard
+iterator myPragma():int=discard
+proc myfun(a:int): int {.myPragma.} = 1
+let a = myfun(1)

tests/errmsgs/undeclared_routime3.nim

@@ -0,0 +1,13 @@
+discard """
+cmd: '''nim c --hints:off $file'''
+errormsg: "undeclared field: 'bar'"
+nimout: '''undeclared_routime3.nim(13, 10) Error: undeclared field: 'bar'
+  found 'undeclared_routime3.bar()[declared in undeclared_routime3.nim(12, 9)]' of kind 'iterator'
+'''
+"""
+
+
+type Foo = object
+var a = Foo()
+iterator bar():int=discard
+let a = a.bar

tests/errmsgs/undeclared_routime4.nim

@@ -0,0 +1,10 @@
+discard """
+cmd: '''nim c --hints:off $file'''
+errormsg: "undeclared field: 'bar'"
+nimout: '''undeclared_routime4.nim(10, 10) Error: undeclared field: 'bar'
+'''
+"""
+
+type Foo = object
+var a = Foo()
+let a = a.bar

tests/errmsgs/undeclared_routime5.nim

@@ -0,0 +1,9 @@
+discard """
+cmd: '''nim c --hints:off $file'''
+errormsg: "undeclared identifier: 'myfun'"
+nimout: '''undeclared_routime5.nim(9, 9) Error: undeclared identifier: 'myfun'
+'''
+"""
+
+
+let a = myfun(1)

tests/errmsgs/undeclared_routime_compiles.nim

@@ -0,0 +1,11 @@
+# D20180828T234921:here
+template foo*(iter: untyped): untyped =
+  when compiles(iter.unexistingField): 0
+  elif compiles(iter.len): 1
+  else: 2
+
+proc foo[A]()=
+  let a2 = @[10, 11]
+  let a3 = foo(pairs(a2))
+
+foo[int]()