record/avfoundation: plug MRC leaks of AVAssetWriter objects and GCD queue

record_avfoundation_t holds five Objective-C object pointers as plain
C struct members:

    AVAssetWriter                         *assetWriter;
    AVAssetWriterInput                    *videoInput;
    AVAssetWriterInput                    *audioInput;
    AVAssetWriterInputPixelBufferAdaptor  *pixelBufferAdaptor;
    dispatch_queue_t                       encodingQueue;

All five are populated via alloc+init (or dispatch_queue_create), each
of which hands back a +1-retained object.

avfoundation_release_handle() cleared these fields with plain

    handle->assetWriter = nil;

Under ARC that is fine because modern clang auto-qualifies ObjC struct
members as __strong and the assignment releases the prior value.

Under MRC the assignment is a bare pointer overwrite - the previously-
retained object is never released. RetroArch builds .m files without
-fobjc-arc in the top-level qb Makefile and in the
RetroArch/_Metal/_OSX107/_iOS13 Xcode projects (only _iOS6/8/9/10/11/
_iOS11_Metal and the Theos iOS build enable ARC globally), so every
record_stop / error-path teardown leaked four AVAssetWriter* objects
and one GCD queue.

Fix with two small helper macros gated on __has_feature(objc_arc):

  * RA_RELEASE_OBJ(field)  -- [field release]; field = nil;   (MRC)
                              field = nil;                    (ARC)
  * RA_RELEASE_DQ(field)   -- dispatch_release + nil on MRC
                              (with a NULL guard since
                              dispatch_release(NULL) is undefined;
                              [nil release] is a safe no-op so the
                              OBJ variant does not need one).

Under ARC both macros expand to the same field-assignment-to-nil the
code already used, so there is no semantic change on that build path.
Under MRC the retain-count arithmetic is now correct.

Also fixes the same leak on the 'canAddInput audio input' error path
in avfoundation_record_init, where the freshly-allocated
handle->audioInput was being dropped with = nil (the alloc+init from
a handful of lines earlier leaked under MRC, then the assetWriter was
used to record video-only).

Thread-safety: unchanged. The release helper is only invoked from
record_free / init error paths on the main thread after the encoding
queue has drained; no concurrent readers of the ivars.

Build matrix impact: this fixes the leak everywhere the file is
compiled as MRC (top-level Makefile macOS builds and the
RetroArch/_Metal/_OSX107/_iOS13 Xcode projects). The ARC builds
(_iOS6/8/9/10/11/_iOS11_Metal + Theos) are unaffected because the ARC
expansion is identical to the old code.

record/drivers/record_avfoundation.m

@@ -33,6 +33,36 @@
 #include "../../retroarch.h"
 #include "../../verbosity.h"
 
+/* Release helpers that work identically under MRC and ARC.
+ *
+ * The ivars on record_avfoundation_t are Objective-C pointers
+ * (AVAssetWriter*, AVAssetWriterInput*, etc. and dispatch_queue_t)
+ * held in a plain C struct.  Modern clang auto-qualifies ObjC struct
+ * members as __strong under ARC, so assignment through them releases
+ * the prior value automatically - plain `field = nil` is correct.
+ *
+ * Under MRC (RetroArch's top-level qb Makefile builds .m files without
+ * -fobjc-arc, and so do the RetroArch/_Metal/_OSX107/_iOS13 Xcode
+ * projects) no such auto-release happens, so `field = nil` would
+ * overwrite a +1-retained pointer and leak the object.  That is the
+ * historical behaviour: every record_stop leaked four AVAssetWriter
+ * objects and one GCD queue.
+ *
+ * Fix with the macros below: explicit release on the MRC path,
+ * assignment-only on the ARC path.  `[nil release]` is a safe no-op,
+ * but `dispatch_release(NULL)` is undefined, so the DQ macro guards.
+ *
+ * The field expression is evaluated twice by the MRC expansion; all
+ * five call sites use a direct struct-member lvalue with no aliasing
+ * so this is safe. */
+#if __has_feature(objc_arc)
+#  define RA_RELEASE_OBJ(_x)  do { (_x) = nil; } while (0)
+#  define RA_RELEASE_DQ(_x)   do { (_x) = nil; } while (0)
+#else
+#  define RA_RELEASE_OBJ(_x)  do { [(_x) release]; (_x) = nil; } while (0)
+#  define RA_RELEASE_DQ(_x)   do { if (_x) { dispatch_release(_x); (_x) = nil; } } while (0)
+#endif
+
 typedef struct record_avfoundation
 {
    AVAssetWriter *assetWriter;
@@ -140,11 +170,11 @@ static void avfoundation_release_handle(record_avfoundation_t *handle)
    if (!handle)
       return;
    scaler_ctx_gen_reset(&handle->scaler);
-   handle->pixelBufferAdaptor = nil;
-   handle->videoInput         = nil;
-   handle->audioInput         = nil;
-   handle->assetWriter        = nil;
-   handle->encodingQueue      = nil;
+   RA_RELEASE_OBJ(handle->pixelBufferAdaptor);
+   RA_RELEASE_OBJ(handle->videoInput);
+   RA_RELEASE_OBJ(handle->audioInput);
+   RA_RELEASE_OBJ(handle->assetWriter);
+   RA_RELEASE_DQ (handle->encodingQueue);
    free(handle);
 }
 
@@ -343,7 +373,7 @@ static void *avfoundation_record_init(const struct record_params *params)
          else
          {
             RARCH_WARN("[AVFoundation] Cannot add audio input, continuing without audio\n");
-            handle->audioInput = nil;
+            RA_RELEASE_OBJ(handle->audioInput);
          }
       }