Bugfix: Allow matching on nkExprEqExpr against varargs[untyped]

This enables macros accepting arbitrary keyword arguments:

log("foo", prop1 = "bar", prop2 = "baz")

As an added bonus, simple templates with varargs arguments can now
forward their params to procs accepting keyword arguments.

compiler/sigmatch.nim

@@ -2173,7 +2173,8 @@ proc matchesAux(c: PContext, n, nOrig: PNode,
   var formal: PSym = if formalLen > 1: m.callee.n.sons[1].sym else: nil
 
   while a < n.len:
-    if a >= formalLen-1 and formal != nil and formal.typ.isVarargsUntyped:
+    if a >= formalLen-1 and f < formalLen and m.callee.n[f].typ.isVarargsUntyped:
+      formal = m.callee.n.sons[f].sym
       incl(marker, formal.position)
       if container.isNil:
         container = newNodeIT(nkArgList, n.sons[a].info, arrayConstr(c, n.info))

tests/overload/tparam_forwarding.nim

@@ -6,6 +6,10 @@ output: '''baz
 a
 b
 c
+x: 1, y: test 1
+x: 2, y: test 2
+x: 10, y: test 3
+x: 4, y: test 4
 '''
 """
 
@@ -35,3 +39,14 @@ templateForwarding fooVarargs, "test".len > 3, Foo(x: 10), Foo(x: 100), Foo(x: 1
 
 procForwarding "a", "b", "c"
 
+proc hasKeywordArgs(x = 10, y = "y") =
+  echo "x: ", x, ", y: ", y
+
+proc hasRegularArgs(x: int, y: string) =
+  echo "x: ", x, ", y: ", y
+
+templateForwarding(hasRegularArgs, true, 1, "test 1")
+templateForwarding(hasKeywordArgs, true, 2, "test 2")
+templateForwarding(hasKeywordArgs, true, y = "test 3")
+templateForwarding(hasKeywordArgs, true, y = "test 4", x = 4)
+