yadif/x86: add prototypes for functions, make code valid C again.

Broken by: libav (a87b17f3)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/x86/yadif.c

@@ -24,6 +24,10 @@
 #include "libavcodec/x86/dsputil_mmx.h"
 #include "libavfilter/yadif.h"
 
+static void yadif_filter_line_ssse3(uint8_t *dst, uint8_t *prev, uint8_t *cur, uint8_t *next, int w, int prefs, int mrefs, int parity, int mode);
+static void yadif_filter_line_sse2(uint8_t *dst, uint8_t *prev, uint8_t *cur, uint8_t *next, int w, int prefs, int mrefs, int parity, int mode);
+static void yadif_filter_line_mmx(uint8_t *dst, uint8_t *prev, uint8_t *cur, uint8_t *next, int w, int prefs, int mrefs, int parity, int mode);
+
 DECLARE_ASM_CONST(16, const xmm_reg, pb_1) = {0x0101010101010101ULL, 0x0101010101010101ULL};
 DECLARE_ASM_CONST(16, const xmm_reg, pw_1) = {0x0001000100010001ULL, 0x0001000100010001ULL};