make libaudioflinger symbols visibility hidden

we export only symbols needed by clients of this library.
this saves about 130KB (1/3rd of the lib size)

Change-Id: Id81f3ecb299ee3abc0811915cf6efe87180bf15c
diff --git a/services/audioflinger/AudioResampler.h b/services/audioflinger/AudioResampler.h
index 2b8694f..29dc5b6 100644
--- a/services/audioflinger/AudioResampler.h
+++ b/services/audioflinger/AudioResampler.h
@@ -19,13 +19,14 @@
 
 #include <stdint.h>
 #include <sys/types.h>
+#include <cutils/compiler.h>
 
 #include <media/AudioBufferProvider.h>
 
 namespace android {
 // ----------------------------------------------------------------------------
 
-class AudioResampler {
+class ANDROID_API AudioResampler {
 public:
     // Determines quality of SRC.
     //  LOW_QUALITY: linear interpolator (1st order)