Add ring_buffer.c to BUILD.gn

Change-Id: I7971f09661e9f87a5dbd28e2657d50692c5bf4f7
diff --git a/BUILD.gn b/BUILD.gn
index 52f4635..42fe2e0 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -4,6 +4,7 @@
     "android-emu/android/base/AlignedBuf.h",
     "android-emu/android/base/Pool.cpp",
     "android-emu/android/base/Pool.h",
+    "android-emu/android/base/ring_buffer.c",
     "android-emu/android/base/SubAllocator.cpp",
     "android-emu/android/base/SubAllocator.h",
     "android-emu/android/base/files/MemStream.cpp",