Make def generated from givens not synthetic

Fixes #12949

Author: odersky

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -783,7 +783,7 @@ object desugar {
         DefDef(
           className.toTermName, joinParams(constrTparams, defParamss),
           classTypeRef, creatorExpr)
-          .withMods(companionMods | mods.flags.toTermFlags & GivenOrImplicit | Synthetic | Final)
+          .withMods(companionMods | mods.flags.toTermFlags & GivenOrImplicit | Final)
           .withSpan(cdef.span) :: Nil
       }
 

tests/pos/i12949.scala

@@ -0,0 +1,19 @@
+object Catch22:
+  trait TC[V]
+  object TC:
+    export Hodor.TC.given
+
+object Hodor:
+  object TC:
+    import Catch22.TC
+    given fromString[V <: String]: TC[V] = ???
+    transparent inline given fromDouble[V <: Double]: TC[V] =
+      new TC[V]:
+        type Out = Double
+    given fromInt[V <: Int]: TC[V] with
+      type Out = Int
+
+object Test:
+  summon[Catch22.TC["hi"]] //works
+  summon[Catch22.TC[7.7]] //works
+  summon[Catch22.TC[1]] //error