[vm] Fix product testing builds

Our product builds (used for testing) are setting dart_runtime_mode ==
"release", so we better align behavior of dart_product_config and 
dart_maybe_product_config in such case otherwise we create unexpected
skew between artifacts and dartaotruntime which is used to compile them.

In reality we should probably delete Product$ARCH build altogether
because all necessary artifacts are actually part of Relase$ARCH builds
anyway these days.

TEST=Run vm-aot-dyn-linux-product-x64 tests


Change-Id: Ifbc2b9679a666c9f22b289d6eb0b8b836a6a6964
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/460040
Commit-Queue: Slava Egorov <vegorov@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>

Author: mraleph

runtime/BUILD.gn

@@ -51,6 +51,9 @@ config("dart_product_config") {
         "-fvisibility=hidden",
       ]
     }
+    if (dart_runtime_mode == "release" && target_os == "linux") {
+      defines += [ "DART_DISABLE_TIMELINE" ]
+    }
   }
 }