ODR violation in cm{CommandArgument,Fortran}Lexer.cxx

Compiling cmake 1.17.2 with gcc 9.3.1 20200506 and linking with ld.bfd 2.34.50.20200519 prints:

[2/46] Linking CXX executable bin/cmake
../Source/LexerParser/cmFortranLexer.cxx:869:8: warning: type ‘struct yyguts_t’ violates the C++ One Definition Rule [-Wodr]
  869 | struct yyguts_t
      |        ^
../Source/LexerParser/cmCommandArgumentLexer.cxx:697:8: note: a different type is defined in another translation unit
  697 | struct yyguts_t
      |        ^
../Source/LexerParser/cmFortranLexer.cxx:873:19: note: the first difference of corresponding definitions is field ‘yyextra_r’
  873 |     YY_EXTRA_TYPE yyextra_r;
      |                   ^
../Source/LexerParser/cmCommandArgumentLexer.cxx:701:19: note: a field of same name but different type is defined in another translation unit
  701 |     YY_EXTRA_TYPE yyextra_r;
      |                   ^
../Source/LexerParser/cmFortranLexer.cxx:869:8: note: type name ‘cmFortranParser_s’ should match type name ‘cmCommandArgumentParserHelper’
  869 | struct yyguts_t
      |        ^
../Source/cmCommandArgumentParserHelper.h:13:7: note: the incompatible type is defined here
   13 | class cmCommandArgumentParserHelper
      |       ^

I use flex 2.6.4 (released 2017)