multimedia/vdr: fix build with clang 16

Since clang 16 (and gcc 11) the default C++ standard is now gnu++17.
Because multimedia/vdr's Makefile does not explicitly set its C++
standard, this leads to an error:

  util.c:269:4: error: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
     register int i;
     ^~~~~~~~~

Because the port's own Makefile is rather non-standard it does not
respect USE_CXXSTD=, so patch away the 'register' keyword instead.

PR:		271707
Approved by:	fernape
MFH:		2023Q2

multimedia/vdr/Makefile

@@ -1,6 +1,6 @@
 PORTNAME=	vdr
 PORTVERSION=	1.7.29
-PORTREVISION=	15
+PORTREVISION=	16
 CATEGORIES=	multimedia
 MASTER_SITES=	ftp://ftp.tvdr.de/vdr/Developer/
 DIST_SUBDIR=	vdr

multimedia/vdr/files/patch-libsi_util.c

@@ -0,0 +1,11 @@
+--- libsi/util.c.orig	2006-02-18 11:17:50 UTC
++++ libsi/util.c
+@@ -266,7 +266,7 @@ u_int32_t CRC32::crc32 (const char *d, int len, u_int3
+
+ u_int32_t CRC32::crc32 (const char *d, int len, u_int32_t crc)
+ {
+-   register int i;
++   int i;
+    const unsigned char *u=(unsigned char*)d; // Saves '& 0xff'
+
+    for (i=0; i<len; i++)