gperf: fix build with clang 16

Clang 16 defaults to C++17, which does not allow the `register` storage
class specifier. This is fixed upstream, but the change doesn’t apply
cleanly to the 3.1 release. Fortunately, the fix is trivial (remove the
disallowed keyword).

pkgs/development/tools/misc/gperf/default.nix

···
     sha256 = "1qispg6i508rq8pkajh26cznwimbnj06wq9sd85vg95v8nwld1aq";
   };
 
+  patches = [
+    # Clang 16 defaults to C++17, which does not allow `register` as a storage class specifier.
+    ./gperf-c++17-register-fix.patch
+  ];
+
   enableParallelBuilding = true;
 
   meta = {

pkgs/development/tools/misc/gperf/gperf-c++17-register-fix.patch

···
+diff --git a/lib/getline.cc b/lib/getline.cc
+index c57c633..0984a7c 100644
+--- a/lib/getline.cc
++++ b/lib/getline.cc
+@@ -55,7 +55,7 @@ getstr (char **lineptr, size_t *n, FILE *stream, char terminator, size_t offset)
+ 
+   for (;;)
+     {
+-      register int c = getc (stream);
++      int c = getc (stream);
+ 
+       /* We always want at least one char left in the buffer, since we
+          always (unless we get an error while reading the first char)