Reduce absolute paths in generated ninja files

testing/libfuzzer/fuzzer_test.gni

Index: testing/libfuzzer/fuzzer_test.gni
diff --git a/testing/libfuzzer/fuzzer_test.gni b/testing/libfuzzer/fuzzer_test.gni
index 014bb8f188cb6af69afcda16034446591340a695..1ab6835c61e1a507ee8fa5d48b4a4a418098e327 100644
--- a/testing/libfuzzer/fuzzer_test.gni
+++ b/testing/libfuzzer/fuzzer_test.gni
@@ -48,16 +48,16 @@ template("fuzzer_test") {
 
         args = [
           "--output",
-          rebase_path(out),
+          rebase_path(out, root_build_dir),
         ]
 
         if (defined(invoker.seed_corpus)) {
-          args += [ rebase_path(invoker.seed_corpus) ]
+          args += [ rebase_path(invoker.seed_corpus, root_build_dir) ]
         }
 
         if (defined(invoker.seed_corpuses)) {
           foreach(seed_corpus_path, invoker.seed_corpuses) {
-            args += [ rebase_path(seed_corpus_path) ]
+            args += [ rebase_path(seed_corpus_path, root_build_dir) ]
           }
         }
 
@@ -93,13 +93,14 @@ template("fuzzer_test") {
         script = "//testing/libfuzzer/gen_fuzzer_config.py"
         args = [
           "--config",
-          rebase_path("$root_build_dir/" + config_name),
+          rebase_path("$root_build_dir/" + config_name, root_build_dir),
         ]
 
         if (defined(invoker.dict)) {
           args += [
             "--dict",
-            rebase_path("$root_build_dir/" + invoker.target_name + ".dict"),
+            rebase_path("$root_build_dir/" + invoker.target_name + ".dict",
+                        root_build_dir),
           ]
         }