avformat/ipfsgateway: define PATH_MAX

PATH_MAX is posix. Some compilers (MSVC) don't define this
thus failing to compile the ipfsgateway file.
Defining it fixes the compile.

Signed-off-by: Mark Gaiser <markg85@gmail.com>
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/ipfsgateway.c

@@ -25,6 +25,12 @@
 #include "os_support.h"
 #include "url.h"
 
+// Define the posix PATH_MAX if not there already.
+// This fixes a compile issue for MSVC.
+#ifndef PATH_MAX
+#define PATH_MAX 4096
+#endif
+
 typedef struct IPFSGatewayContext {
     AVClass *class;
     URLContext *inner;