cache lookup of any2stringaddMethod

`any2stringadd` is an implicit class, and the implicit class creates a factory method `def any2stringadd[A](a: A)` and since it's a SIP-15 value class there's a companion named `any2stringadd` too!

Author: eed3si9n

src/compiler/scala/tools/nsc/typechecker/Contexts.scala

@@ -856,7 +856,7 @@ trait Contexts { self: Analyzer =>
       !({
         // [eed3si9n] ideally I'd like to do this: val fd = settings.isScala214 && sym.isDeprecated
         // but implicit caching currently does not report sym.isDeprecated correctly.
-        val fd = settings.isScala214 && (name ne null) && definitions.isPredefMemberNamed(sym, TermName("any2stringadd"))
+        val fd = settings.isScala214 && (sym == currentRun.runDefinitions.Predef_any2stringaddMethod)
         if (settings.XlogImplicits && fd) echo(sym.pos, sym + " is not a valid implicit value because:\n" + "-Xsource:2.14 removes scala.Predef.any2stringadd")
         fd
       }) &&

src/reflect/scala/reflect/internal/Definitions.scala

@@ -1504,6 +1504,7 @@ trait Definitions extends api.StandardDefinitions {
       lazy val Predef_classOf      = getMemberMethod(PredefModule, nme.classOf)
       lazy val Predef_implicitly   = getMemberMethod(PredefModule, nme.implicitly)
       lazy val Predef_???          = DefinitionsClass.this.Predef_???
+      lazy val Predef_any2stringaddMethod = PredefModule.info.decl(nme.any2stringadd.toTermName).suchThat(_.isMethod)
 
       lazy val arrayApplyMethod       = getMemberMethod(ScalaRunTimeModule, nme.array_apply)
       lazy val arrayUpdateMethod      = getMemberMethod(ScalaRunTimeModule, nme.array_update)

src/reflect/scala/reflect/internal/StdNames.scala

@@ -491,7 +491,7 @@ trait StdNames {
       if (isConstructorName(name))
         DEFAULT_GETTER_INIT_STRING + pos
       else
-        name + DEFAULT_GETTER_STRING + pos
+        name.toString + DEFAULT_GETTER_STRING + pos
     )
     // Nominally, name from name$default$N, CONSTRUCTOR for <init>
     def defaultGetterToMethod(name: Name): TermName = (
@@ -654,6 +654,7 @@ trait StdNames {
     val accessor: NameType             = "accessor"
     val add_ : NameType                = "add"
     val annotation: NameType           = "annotation"
+    val any2stringadd: NameType        = "any2stringadd"
     val anyHash: NameType              = "anyHash"
     val anyValClass: NameType          = "anyValClass"
     val apply: NameType                = "apply"