Added std/effecttraits.nim (#15462)

lib/std/effecttraits.nim

@@ -0,0 +1,19 @@
+#
+#
+#            Nim's Runtime Library
+#        (c) Copyright 2018 Nim contributors
+#
+#    See the file "copying.txt", included in this
+#    distribution, for details about the copyright.
+#
+
+## This module provides access to the inferred .raises effects
+## for Nim's macro system.
+
+import macros
+
+proc getRaisesListImpl(n: NimNode): NimNode = discard "see compiler/vmops.nim"
+
+proc getRaisesList*(call: NimNode): NimNode =
+  expectKind call, nnkCallKinds
+  result = getRaisesListImpl(call[0])