Move function declaration from C source to header file

Index: audio/audio.h
===================================================================
@@ -87,6 +87,9 @@
     uint64_t old_ts;
 } QEMUAudioTimeStamp;
 
+int wav_start_capture (CaptureState *s, const char *path, int freq,
+                       int bits, int nchannels);
+
 void AUD_vlog (const char *cap, const char *fmt, va_list ap);
 void AUD_log (const char *cap, const char *fmt, ...)
 #ifdef __GNUC__

Index: monitor.c
===================================================================
@@ -1264,9 +1264,6 @@
 }
 
 #ifdef HAS_AUDIO
-int wav_start_capture (CaptureState *s, const char *path, int freq,
-                       int bits, int nchannels);
-
 static void do_wav_capture (const char *path,
                             int has_freq, int freq,
                             int has_bits, int bits,