Snippets for mapnik 4.3.0 from Nix x86_64-linux

Sourced from https://hydra.nixos.org/log/zpp9r652m03q9rpgg1frknc2d4767f57-mapnik-4.3.0.drv.

/build/source/src/image.cpp:88:29: warning: type attributes ignored after type is already defined [-Wattributes]
   88 | template struct MAPNIK_DECL image_dimensions<4294836225>;
      |                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

/build/source/include/mapnik/xml_loader.hpp:33:19: warning: type attributes ignored after type is already defined [-Wattributes]
   33 | class MAPNIK_DECL xml_node;
      |                   ^~~~~~~~

/build/source/plugins/input/geobuf/geobuf_datasource.cpp:99:15: warning: ignoring return value of 'size_t fread(void*, size_t, size_t, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   99 |     std::fread(geobuf.data(), in.size(), 1, in.get());
      |     ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

/nix/store/m300ngckdmal8wnl3bjbpwca3a5bn74c-glibc-2.42-67-dev/include/bits/string_fortified.h:29:33: warning: 'void* __builtin___memcpy_chk(void*, const void*, long unsigned int, long unsigned int)' writing between 129 and 4294967295 bytes into a region of size 128 overflows the destination [-Wstringop-overflow=]
   29 |   return __builtin___memcpy_chk (__dest, __src, __len,
      |          ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
   30 |                                  __glibc_objsize0 (__dest));
      |                                  ~~~~~~~~~~~~~~~~~~~~~~~~~~

/build/source/build/test/cleanup.hpp:30:30: warning: 'void xmlCleanupEncodingAliases()' is deprecated: See https://gnome.pages.gitlab.gnome.org/libxml2/html/deprecated.html [-Wdeprecated-declarations]
   30 |     xmlCleanupEncodingAliases();
      |     ~~~~~~~~~~~~~~~~~~~~~~~~~^~

/build/source/test/unit/datasource/topojson.cpp:43:15: warning: ignoring return value of 'size_t fread(void*, size_t, size_t, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   43 |     std::fread(&buffer[0], buffer.size(), 1, file.get());
      |     ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

/build/source/test/visual/../cleanup.hpp:30:30: warning: 'void xmlCleanupEncodingAliases()' is deprecated: See https://gnome.pages.gitlab.gnome.org/libxml2/html/deprecated.html [-Wdeprecated-declarations]
   30 |     xmlCleanupEncodingAliases();
      |     ~~~~~~~~~~~~~~~~~~~~~~~~~^~