[build] Fix build failures in Chrome

Use relative paths to access v8 root build rules since // means
something different in a chrome build.

Bug: v8:7330
Change-Id: I4eac73b394daaf0250b0fa2ad415af560b03c114
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2856840
Commit-Queue: Dan Elphick <delphick@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Auto-Submit: Dan Elphick <delphick@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74258}

tools/v8windbg/BUILD.gn

@@ -54,10 +54,10 @@ v8_shared_library("v8windbg") {
 
   deps = [
     ":v8windbg_base",
+    "../../:v8_flags",
+    "../../:v8_libbase",
+    "../../:v8_shared_internal_headers",
     "../debug_helper:v8_debug_helper",
-    "//:v8_flags",
-    "//:v8_libbase",
-    "//:v8_shared_internal_headers",
   ]
 }