Rethrow SuspendExceptions caught in CodeGen phase (scala#22009)

Related PR: scala#21651
There, a mechanism was added to the Phase classes, where any phase could
catch a SuspendException and have a compilation unit suspended (stopped
and recompiled later). In this fix, we rethrow incorrectly caught
SuspendExceptions, so that the aforementioned mechanism can take care of
the rest.
Fixes: scala#21983

compiler/src/dotty/tools/backend/jvm/CodeGen.scala

@@ -84,6 +84,7 @@ class CodeGen(val int: DottyBackendInterface, val primitives: DottyPrimitives)(
         registerGeneratedClass(mirrorClassNode, isArtifact = true)
       catch
         case ex: InterruptedException => throw ex
+        case ex: CompilationUnit.SuspendException => throw ex
         case ex: Throwable =>
           ex.printStackTrace()
           report.error(s"Error while emitting ${unit.source}\n${ex.getMessage}", NoSourcePosition)

tests/pos-macros/i21983/Test.scala

@@ -0,0 +1,13 @@
+package example
+
+sealed trait Test
+
+object Test {
+  case object Foo extends Test
+
+  val visitorType = mkVisitorType[Test]
+
+  trait Visitor[A] {
+    type V[a] = visitorType.Out[a]
+  }
+}

tests/pos-macros/i21983/UsesTest.scala

@@ -0,0 +1,3 @@
+package example
+
+val _ = Test.Foo

tests/pos-macros/i21983/VisitorMacros.scala

@@ -0,0 +1,13 @@
+package example
+
+import scala.deriving.Mirror
+import scala.quoted.*
+
+private def mkVisitorTypeImpl[T: Type](using q: Quotes): Expr[VisitorType[T]] =
+  '{new VisitorType[T]{}}
+
+transparent inline def mkVisitorType[T]: VisitorType[T] = ${ mkVisitorTypeImpl[T] }
+
+trait VisitorType[T] {
+  type Out[A]
+}