avisynth: ifdef to avoid implicit function declaration errors

The demuxer doesn't use these functions, so it shouldn't affect
anything.  Investigate whether this can be fixed by how headers
are checked in configure.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

compat/avisynth/avisynth_c.h

@@ -357,11 +357,13 @@ AVSC_INLINE void avs_set_fps(AVS_VideoInfo * p, unsigned numerator, unsigned den
     p->fps_denominator = denominator/x;
 }
 
+#ifdef AVS_IMPLICIT_FUNCTION_DECLARATION_ERROR
 AVSC_INLINE int avs_is_same_colorspace(AVS_VideoInfo * x, AVS_VideoInfo * y)
 {
         return (x->pixel_type == y->pixel_type)
                 || (avs_is_yv12(x) && avs_is_yv12(y));
 }
+#endif
 
 /////////////////////////////////////////////////////////////////////
 //
@@ -400,8 +402,10 @@ typedef struct AVS_VideoFrame {
 // Access functions for AVS_VideoFrame
 AVSC_API(int, avs_get_pitch_p)(const AVS_VideoFrame * p, int plane);
 
+#ifdef AVS_IMPLICIT_FUNCTION_DECLARATION_ERROR
 AVSC_INLINE int avs_get_pitch(const AVS_VideoFrame * p) {
         return avs_get_pitch_p(p, 0);}
+#endif
 
 AVSC_API(int, avs_get_row_size_p)(const AVS_VideoFrame * p, int plane);
 
@@ -415,15 +419,19 @@ AVSC_INLINE int avs_get_height(const AVS_VideoFrame * p) {
 
 AVSC_API(const BYTE *, avs_get_read_ptr_p)(const AVS_VideoFrame * p, int plane);
 
+#ifdef AVS_IMPLICIT_FUNCTION_DECLARATION_ERROR
 AVSC_INLINE const BYTE* avs_get_read_ptr(const AVS_VideoFrame * p) {
         return avs_get_read_ptr_p(p, 0);}
+#endif
 
 AVSC_API(int, avs_is_writable)(const AVS_VideoFrame * p);
 
 AVSC_API(BYTE *, avs_get_write_ptr_p)(const AVS_VideoFrame * p, int plane);
 
+#ifdef AVS_IMPLICIT_FUNCTION_DECLARATION_ERROR
 AVSC_INLINE BYTE* avs_get_write_ptr(const AVS_VideoFrame * p) {
         return avs_get_write_ptr_p(p, 0);}
+#endif
 
 AVSC_API(void, avs_release_video_frame)(AVS_VideoFrame *);
 // makes a shallow copy of a video frame