Avoid running sepparate compilation tests under legacy tests

Those tests have never fully been supported, all files are compiled
at the same time.

Author: nicolasstucki

compiler/test/dotty/tools/dotc/CompilerTest.scala

@@ -109,8 +109,12 @@ abstract class CompilerTest {
     if (runTest)
       log(s"WARNING: run tests can only be run by partest, JUnit just verifies compilation: $prefix$dirName")
     val (filePaths, javaFilePaths, normArgs, expErrors) = computeFilePathsAndExpErrors
-    compileWithJavac(javaFilePaths, Array.empty) // javac needs to run first on dotty-library
-    compileArgs(javaFilePaths ++ filePaths ++ normArgs, expErrors)
+    if (filePaths.exists(_.endsWith("_1.scala"))) {
+      log(s"WARNING: separate compilation test can not be run as legacy test: $prefix$dirName")
+    } else {
+      compileWithJavac(javaFilePaths, Array.empty) // javac needs to run first on dotty-library
+      compileArgs(javaFilePaths ++ filePaths ++ normArgs, expErrors)
+    }
   }
   def runDir(prefix: String, dirName: String, args: List[String] = Nil)
       (implicit defaultOptions: List[String]): Unit =