cocoa_common: gate VoiceOver @available on 10.13 SDK

GCC 4.0 (Xcode 3.1, PowerPC) reports:

    cocoa_common.m:77: error: stray '@' in program

@available(...) is a clang-only Obj-C extension (Xcode 7+, 2015).
GCC 4.0 sees the '@' followed by a non-keyword identifier and bails.
Same class of issue as the platform_darwin.m fixes in 2b51544,
6c80736, 27a843f, 2df15df.

RAIsVoiceOverRunning() is called from configuration.c and needs to
exist on every Cocoa build.  NSWorkspace's isVoiceOverEnabled
property is 10.13+; on older SDKs it doesn't exist anyway, so the
only sensible behavior there is to return false.

Wrap the @available block in #if MAC_OS_X_VERSION_MAX_ALLOWED >=
101300.  On 10.5-10.12 SDKs the block is preprocessed out entirely
and the function falls through to the existing 'return false'.
On 10.13+ SDKs (modern clang), behavior is unchanged.

The other 10 @available sites in this file are already preprocessed
out on macOS — they sit inside TARGET_OS_IOS, TARGET_OS_TV,
HAVE_COCOATOUCH, or SDK-version gates that only trigger on newer
build configurations.

Author: LibretroAdmin

ui/drivers/cocoa/cocoa_common.m

@@ -74,8 +74,14 @@ extern bool RAIsVoiceOverRunning(void)
 #import <AppKit/AppKit.h>
 extern bool RAIsVoiceOverRunning(void)
 {
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= 101300
+   /* @available is clang-only (Xcode 7+).  GCC 4.0 rejects the
+    * '@' as a stray token.  isVoiceOverEnabled on NSWorkspace is
+    * 10.13+ anyway, so on older SDKs we skip this block entirely
+    * and fall through to the return below. */
    if (@available(macOS 10.13, *))
       return [[NSWorkspace sharedWorkspace] isVoiceOverEnabled];
+#endif
    return false;
 }
 #endif