audio/din: Fix build failures for clang 16.0.6

Remove "register" keyword, which is not supported in ISO C++17.

Change applies to 14.0-CURRENT (1400092 and above).

audio/din/files/patch-src_RtAudio.cpp

@@ -0,0 +1,17 @@
+Add support for compiling in ISO C++17
+--- src/RtAudio.cpp.orig	2023-07-15 17:18:23 UTC
++++ src/RtAudio.cpp
+@@ -10050,8 +10050,13 @@ void RtApi :: byteSwapBuffer( char *buffer, unsigned i
+
+ void RtApi :: byteSwapBuffer( char *buffer, unsigned int samples, RtAudioFormat format )
+ {
++  #if __cplusplus < 201703L
+   register char val;
+   register char *ptr;
++  #else
++  char val;
++  char *ptr;
++  #endif
+
+   ptr = buffer;
+   if ( format == RTAUDIO_SINT16 ) {