Build fails with LTO

[eli-schwartz]

Using the CXXFLAGS: -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing

/bin/sh ../libtool  --tag=CXX   --mode=link x86_64-pc-linux-gnu-g++  -march=native -fstack-protector-all -O2 -pipe -fdiagnostics-color=always -frecord-gcc-switches -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=3 -fstack-clash-protection -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing  -Wformat -Werror=format-security -Wall  -no-undefined -version-info 2:0:0 -Wl,-O1 -Wl,--as-needed -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing -Wl,--defsym=__gentoo_check_ldflags__=0 -o libmecab.la -rpath /usr/lib64 viterbi.lo tagger.lo utils.lo eval.lo iconv_utils.lo dictionary_rewriter.lo dictionary_generator.lo dictionary_compiler.lo context_id.lo connector.lo nbest_generator.lo writer.lo string_buffer.lo param.lo tokenizer.lo char_property.lo dictionary.lo feature_index.lo lbfgs.lo learner_tagger.lo learner.lo libmecab.lo  -lpthread -lpthread  -lstdc++ 
libtool: link: x86_64-pc-linux-gnu-g++  -fPIC -DPIC -shared -nostdlib /usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../lib64/crti.o /usr/lib/gcc/x86_64-pc-linux-gnu/13/crtbeginS.o  .libs/viterbi.o .libs/tagger.o .libs/utils.o .libs/eval.o .libs/iconv_utils.o .libs/dictionary_rewriter.o .libs/dictionary_generator.o .libs/dictionary_compiler.o .libs/context_id.o .libs/connector.o .libs/nbest_generator.o .libs/writer.o .libs/string_buffer.o .libs/param.o .libs/tokenizer.o .libs/char_property.o .libs/dictionary.o .libs/feature_index.o .libs/lbfgs.o .libs/learner_tagger.o .libs/learner.o .libs/libmecab.o   -Wl,--as-needed -lpthread -L/usr/lib/gcc/x86_64-pc-linux-gnu/13 -L/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../x86_64-pc-linux-gnu/lib -L/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../.. -lstdc++ -lm -lc -lgcc_s /usr/lib/gcc/x86_64-pc-linux-gnu/13/crtendS.o /usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../lib64/crtn.o  -march=native -fstack-protector-all -O2 -fdiagnostics-color=always -frecord-gcc-switches -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing -Werror=format-security -Wl,-O1 -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing -Wl,--defsym=__gentoo_check_ldflags__=0   -Wl,-soname -Wl,libmecab.so.2 -o .libs/libmecab.so.2.0.0
iconv_utils.h:19:7: error: type 'struct Iconv' violates the C++ One Definition Rule [-Werror=odr]
   19 | class Iconv {
      |       ^
iconv_utils.h:19:7: note: a different type is defined in another translation unit
   19 | class Iconv {
      |       ^
iconv_utils.h:22:11: note: the first difference of corresponding definitions is field 'ic_'
   22 |   iconv_t ic_;
      |           ^
iconv_utils.h:24:7: note: a field of same name but different type is defined in another translation unit
   24 |   int ic_;
      |       ^
iconv_utils.h:19:7: note: type 'void *' should match type 'int'
   19 | class Iconv {
      |       ^
iconv_utils.h:36:8: error: type of 'convert' does not match original declaration [-Werror=lto-type-mismatch]
   36 |   bool convert(std::string *);
      |        ^
iconv_utils.cpp:110:6: note: 'convert' was previously declared here
  110 | bool Iconv::convert(std::string *str) {
      |      ^
iconv_utils.cpp:110:6: note: code may be misoptimized unless '-fno-strict-aliasing' is used
lto1: some warnings being treated as errors
lto-wrapper: fatal error: x86_64-pc-linux-gnu-g++ returned 1 exit status

Downstream report: https://bugs.gentoo.org/924569
Full logs: build.log