Retry server errors in dependency downloader (#4458)

shared/src/main/kotlin/org/jetbrains/kotlin/konan/util/DependencyDownloader.kt

@@ -175,13 +175,7 @@ class DependencyDownloader(
 
         var attempt = 1
         var waitTime = 0L
-        while (true) {
+        val handleException = { e: Exception ->
-            try {
-                tryDownload(source, tmpFile)
-                break
-            } catch (e: HTTPResponseException) {
-                throw e
-            } catch (e: IOException) {
             if (attempt >= maxAttempts) {
                 throw e
             }
@@ -192,6 +186,21 @@ class DependencyDownloader(
             // TODO: Wait better
             Thread.sleep(waitTime)
         }
+        while (true) {
+            try {
+                tryDownload(source, tmpFile)
+                break
+            } catch (e: HTTPResponseException) {
+                if (e.responseCode >= 500) {
+                    // Retry server errors.
+                    handleException(e)
+                } else {
+                    // Do not retry client errors.
+                    throw e
+                }
+            } catch (e: IOException) {
+                handleException(e)
+            }
         }
 
         Files.move(tmpFile.toPath(), destination.toPath(), StandardCopyOption.REPLACE_EXISTING)