Add fuzzer_common.c

Apparently the header file alone wasn't sufficient for the
buildflags used by the bots.

Change-Id: I98ca8397234b0cc09c48cf0dc3635800a8c548ef
diff --git a/BUILD.gn b/BUILD.gn
index b34dfdd..ac133db 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -140,6 +140,9 @@
   }
 
   if (use_fuzzing_engine) {
-    sources += [ "oss-fuzz/fuzzer_common.h" ]
+    sources += [
+      "oss-fuzz/fuzzer_common.c",
+      "oss-fuzz/fuzzer_common.h",
+    ]
   }
 }
diff --git a/README.chromium b/README.chromium
index 9717c3e..4ddff33 100644
--- a/README.chromium
+++ b/README.chromium
@@ -6,7 +6,9 @@
 Security Critical: yes
 
 Description:
-This is a straight dump of flac-1.4.2 with all the unused files removed.
+This is a straight dump of flac-1.4.2 with all the unused files removed. One
+file has been added (oss-fuzz/fuzzer_common.c) to allow Chromium fuzzers to
+link properly.
 
 This library is required for the browser to compress and encode recorded audio
 before sending to Google servers for speech recognition. It is also used to
diff --git a/oss-fuzz/fuzzer_common.c b/oss-fuzz/fuzzer_common.c
new file mode 100644
index 0000000..a6e9777
--- /dev/null
+++ b/oss-fuzz/fuzzer_common.c
@@ -0,0 +1,9 @@
+// Copyright 2023 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <stdint.h>
+#include "fuzzer_common.h"
+
+// Stub file binding fuzzer specific externs from `fuzzer_common.h` to ensure
+// that fuzzers link properly.