Use av_strdup instead of strdup, fixes mingw build

libavfilter/libmpcodecs/vf_detc.c

@@ -16,7 +16,6 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#define _BSD_SOURCE //strdup
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -413,7 +412,7 @@ static void parse_var(struct vf_priv_s *p, char *var)
 static void parse_args(struct vf_priv_s *p, char *args)
 {
         char *next, *orig;
-        for (args=orig=strdup(args); args; args=next) {
+        for (args=orig=av_strdup(args); args; args=next) {
                 next = strchr(args, ':');
                 if (next) *next++ = 0;
                 parse_var(p, args);

libavfilter/libmpcodecs/vf_divtc.c

@@ -16,7 +16,6 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#define _BSD_SOURCE //strdup
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -601,7 +600,7 @@ static int vf_open(vf_instance_t *vf, char *args)
    struct vf_priv_s *p;
    char *filename="framediff.log", *ap, *q, *a;
 
-   if(args && !(args=strdup(args)))
+   if(args && !(args=av_strdup(args)))
       {
    nomem:
       mp_msg(MSGT_VFILTER, MSGL_FATAL,