opensp: fix build with clang 16

pkgs/tools/text/sgml/opensp/default.nix

@@ -1,5 +1,6 @@
 { lib, stdenv, fetchurl, fetchpatch, xmlto, docbook_xml_dtd_412
 , libxslt, docbook_xsl, autoconf, automake, gettext, libiconv, libtool
+, autoreconfHook
 }:
 
 stdenv.mkDerivation rec {
@@ -21,6 +22,8 @@ stdenv.mkDerivation rec {
       url = "https://gitweb.gentoo.org/repo/gentoo.git/plain/app-text/opensp/files/opensp-1.5.2-c11-using.patch?id=688d9675782dfc162d4e6cff04c668f7516118d0";
       sha256 = "04q14s8qsad0bkjmj067dn831i0r6v7742rafdlnbfm5y249m2q6";
     })
+    # Clang 16 defaults to C++17, which does not allow `register` as a storage class specifier.
+    ./fix-register-storage-class.patch
   ];
 
   setupHook = ./setup-hook.sh;
@@ -41,7 +44,11 @@ stdenv.mkDerivation rec {
     xmlto
     docbook_xml_dtd_412
     docbook_xsl
-  ] ++ lib.optionals stdenv.isCygwin [ autoconf automake libtool ];
+  ]
+  # Clang 16 fails to build due to inappropriate definitions in the `config.h` generated by the
+  # existing configure scripts. Regenerate them to make sure they detect its features correctly.
+  ++ lib.optional stdenv.cc.isClang autoreconfHook
+  ++ lib.optionals stdenv.isCygwin [ autoconf automake libtool ];
 
   doCheck = false; # fails
 

pkgs/tools/text/sgml/opensp/fix-register-storage-class.patch

@@ -0,0 +1,11 @@
+--- a/lib/Recognizer.cxx	2005-11-05 04:05:20.000000000 -0500
++++ b/lib/Recognizer.cxx	2023-06-03 11:45:04.497116217 -0400
+@@ -39,7 +39,7 @@
+   }
+   else
+     in->startTokenNoMulticode();
+-  register const Trie *pos = trie_.pointer();
++  const Trie *pos = trie_.pointer();
+   do {
+     pos = pos->next(map_[in->tokenChar(mgr)]);
+   } while (pos->hasNext());