Fix -Wimplicit-function-declaration and -Wincompatible-pointer-types errors
with gcc 14.

Examples of errors:

```
daphne/daphne-1.0-src/vldp2/vldp/vldp_internal.c: In function 'idle_handler_precache':
daphne/daphne-1.0-src/vldp2/vldp/vldp_internal.c:852:31: error: implicit declaration of function 'fileno' [-Wimplicit-function-declaration]
  852 |                         fstat(fileno(F), &filestats);   // get stats for file to get file length
      |                               ^~~~~~
```

```
daphne/src/thread/pthread/SDL_systhread.c:104:24: error: passing argument 1 of 'pthread_create' from incompatible pointer type [-Wincompatible-pointer-types]
  104 |     if (pthread_create(&thread->handle, &type, RunThread, args) != 0) {
      |                        ^~~~~~~~~~~~~~~
      |                        |
      |                        SYS_ThreadHandle * {aka int *}
In file included from daphne/src/thread/pthread/SDL_systhread.c:24:
/usr/include/pthread.h:80:20: note: expected 'struct __pthread ** restrict' but argument is of type 'SYS_ThreadHandle *' {aka 'int *'}
   80 | int pthread_create(pthread_t *__restrict, const pthread_attr_t *__restrict, void *(*)(void *), void *__restrict);
      |                    ^
```

--- a/daphne/daphne-1.0-src/vldp2/vldp/vldp_internal.c
+++ b/daphne/daphne-1.0-src/vldp2/vldp/vldp_internal.c
@@ -29,6 +29,7 @@

 #include <stdint.h>

+#define _DEFAULT_SOURCE
 #include <stdio.h>
 #include <stdlib.h>	// for malloc/free
 #include <string.h>
--- a/daphne/src/audio/SDL_audiocvt.c
+++ b/daphne/src/audio/SDL_audiocvt.c
@@ -18,6 +18,7 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
+#include <math.h>
 #include <stdint.h>
 #include "../SDL_internal.h"

--- a/daphne/src/thread/pthread/SDL_systhread.c
+++ b/daphne/src/thread/pthread/SDL_systhread.c
@@ -29,10 +29,12 @@

 #include <signal.h>

+#define _BSD_SOURCE
+#include <sys/syscall.h>
+
 #ifdef __LINUX__
 #include <sys/time.h>
 #include <sys/resource.h>
-#include <sys/syscall.h>
 #include <unistd.h>
 #endif /* __LINUX__ */

@@ -98,7 +100,8 @@
     }

     /* Create the thread and go! */
-    if (pthread_create(&thread->handle, &type, RunThread, args) != 0) {
+    if (pthread_create((struct __pthread ** restrict) &thread->handle, &type,
+        RunThread, args) != 0) {
 		// 2017.02.07 - RJS ADD - Logging.
         return SDL_SetError("Not enough resources to create thread");
     }
@@ -207,13 +210,13 @@
 void
 SDL_SYS_WaitThread(SDL_Thread * thread)
 {
-    pthread_join(thread->handle, 0);
+    pthread_join((struct __pthread *) thread->handle, 0);
 }

 void
 SDL_SYS_DetachThread(SDL_Thread * thread)
 {
-    pthread_detach(thread->handle);
+    pthread_detach((struct __pthread *) thread->handle);
 }

 /* vi: set ts=4 sw=4 expandtab: */