Move @ _* to : _* error under -strict

Projects that cross-compile with Scala 2 cannot use the new syntax, and
are therefore forced to set `-language:Scala2` currently even if they
don't need any of the other changes enabled by this flag to compile.

Author: smarter

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -1858,14 +1858,16 @@ object Parsers {
         // compatibility for Scala2 `x @ _*` syntax
         infixPattern() match {
           case pt @ Ident(tpnme.WILDCARD_STAR) =>
-            migrationWarningOrError("The syntax `x @ _*' is no longer supported; use `x : _*' instead", startOffset(p))
+            if (ctx.settings.strict.value)
+              migrationWarningOrError("The syntax `x @ _*' is no longer supported; use `x : _*' instead", startOffset(p))
             atSpan(startOffset(p), offset) { Typed(p, pt) }
           case pt =>
             atSpan(startOffset(p), 0) { Bind(name, pt) }
         }
       case p @ Ident(tpnme.WILDCARD_STAR) =>
         // compatibility for Scala2 `_*` syntax
-        migrationWarningOrError("The syntax `_*' is no longer supported; use `x : _*' instead", startOffset(p))
+        if (ctx.settings.strict.value)
+          migrationWarningOrError("The syntax `_*' is no longer supported; use `x : _*' instead", startOffset(p))
         atSpan(startOffset(p)) { Typed(Ident(nme.WILDCARD), p) }
       case p =>
         p