avutil/file_open: avoid file handle inheritance on Windows

Avoids inheritance of file handles on Windows systems similar to the
O_CLOEXEC/FD_CLOEXEC flag on Linux.

Fixes file lock issues in Windows applications when a child process
is started with handle inheritance enabled (standard input/output
redirection) while a FFmpeg transcoding is running in the parent
process.

Links relevant to the subject:

https://msdn.microsoft.com/en-us/library/w7sa2b22.aspx

Describes the _wsopen() function and the O_NOINHERIT flag. File handles
opened by _wsopen() are inheritable by default.

https://msdn.microsoft.com/en-us/library/windows/desktop/ms682425%28v=vs.85%29.aspx

Describes handle inheritance when creating new processes. Handle
inheritance must be enabled (bInheritHandles = TRUE) e.g. when you want
to pass handles for stdin/stdout via lpStartupInfo.
Signed-off-by: Tobias Rapp <t.rapp@noa-audio.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavutil/file_open.c

@@ -77,6 +77,9 @@ int avpriv_open(const char *filename, int flags, ...)
 #ifdef O_CLOEXEC
     flags |= O_CLOEXEC;
 #endif
+#ifdef O_NOINHERIT
+    flags |= O_NOINHERIT;
+#endif
 
     fd = open(filename, flags, mode);
 #if HAVE_FCNTL