poco : 1.12.2-all 

# uname -a
SunOS solaris10 5.10 Generic_147148-26 i86pc i386 i86pc Solaris

# gcc --version
gcc (GCC) 5.2.0
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

# cmake --version
cmake version 3.6.3

CMake suite maintained and supported by Kitware (kitware.com/cmake).

# make --version
make: Schily-Tools Parallel Make 1.1 solaris2.10-i386 2020/03/28
    derived from SunPro Make sources

Copyright (C) 1987-2006 Sun Microsystems
Copyright (C) 1996-2020 Joerg Schilling

Building CXX object Foundation/CMakeFiles/Foundation.dir/src/Var.cpp.o

...

In file included from /export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/Foundation/include/Poco/Dynamic/Var.h:26:0,
             from /export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/Foundation/src/Var.cpp:15:
/export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/Foundation/include/Poco/Dynamic/VarHolder.h:218:15: error: 
'virtual void Poco::Dynamic::VarHolder::convert(char&) const' cannot be overloaded
  virtual void convert(char& val) const;
           ^
/export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/Foundation/include/Poco/Dynamic/VarHolder.h:138:15: error: with 'virtual void Poco::Dynamic::VarHolder::convert(Poco::Int8&) const'
  virtual void convert(Int8& val) const;
           ^
/export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/Foundation/include/Poco/Dynamic/VarHolder.h:590:13: error: redefinition of 'void Poco::Dynamic::VarHolder::convert(char&) const'
 inline void VarHolder::convert(char& /*val*/) const

... 

In file included from /export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/Foundation/src/Var.cpp:15:0:
/export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/Foundation/include/Poco/Dynamic/Var.h: In function 'Poco::Int8 
Poco::Dynamic::operator+(const Int8&, const Poco::Dynamic::Var&)':
/export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/Foundation/include/Poco/Dynamic/Var.h:968:19: error: redefinition of 'Poco::Int8 Poco::Dynamic::operator+(const Int8&, const Poco::Dynamic::Var&)'
inline Poco::Int8 operator + (const Poco::Int8& other, const Var& da)
               ^
/export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/Foundation/include/Poco/Dynamic/Var.h:864:13: note: 'char 
Poco::Dynamic::operator+(const char&, const Poco::Dynamic::Var&)' previously defined here
 inline char operator + (const char& other, const Var& da)
         ^
/export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/Foundation/include/Poco/Dynamic/Var.h: In function 'Poco::Int8 
Poco::Dynamic::operator-(const Int8&, const Poco::Dynamic::Var&)':
/export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/Foundation/include/Poco/Dynamic/Var.h:975:19: error: redefinition of 'Poco::Int8 Poco::Dynamic::operator-(const Int8&, const Poco::Dynamic::Var&)'
 inline Poco::Int8 operator - (const Poco::Int8& other, const Var& da)
               ^
/export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/Foundation/include/Poco/Dynamic/Var.h:871:13: note: 'char 
Poco::Dynamic::operator-(const char&, const Poco::Dynamic::Var&)' previously defined here
 inline char operator - (const char& other, const Var& da) 

...
/export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/Foundation/include/Poco/Dynamic/Struct.h:700:7: error: 'void 
Poco::Dynamic::VarHolderImpl<Poco::Dynamic::Struct<std::__cxx11::basic_string<char>, 
tsl::ordered_map<std::__cxx11::basic_string<char>, Poco::Dynamic::Var, std::hash<std::__cxx11::basic_string<char> >, 
std::equal_to<std::__cxx11::basic_string<char> >, std::allocator<std::pair<std::__cxx11::basic_string<char>, Poco::Dynamic::Var> >, 
std::deque<std::pair<std::__cxx11::basic_string<char>, Poco::Dynamic::Var>, std::allocator<std::pair<std::__cxx11::basic_string<char>, 
Poco::Dynamic::Var> > > >, tsl::ordered_set<std::__cxx11::basic_string<char>, std::hash<std::__cxx11::basic_string<char> >, 
std::equal_to<std::__cxx11::basic_string<char> >, std::allocator<std::__cxx11::basic_string<char> >, 
std::deque<std::__cxx11::basic_string<char>, std::allocator<std::__cxx11::basic_string<char> > > > > >::convert(char&) const' cannot be overloaded
  void convert(char&) const
   ^
/export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/Foundation/include/Poco/Dynamic/Struct.h:645:7: error: with 'void Poco::Dynamic::VarHolderImpl<Poco::Dynamic::Struct<std::__cxx11::basic_string<char>, 
tsl::ordered_map<std::__cxx11::basic_string<char>, Poco::Dynamic::Var, std::hash<std::__cxx11::basic_string<char> >, 
std::equal_to<std::__cxx11::basic_string<char> >, std::allocator<std::pair<std::__cxx11::basic_string<char>, Poco::Dynamic::Var> >, 
std::deque<std::pair<std::__cxx11::basic_string<char>, Poco::Dynamic::Var>, std::allocator<std::pair<std::__cxx11::basic_string<char>, 
Poco::Dynamic::Var> > > >, tsl::ordered_set<std::__cxx11::basic_string<char>, std::hash<std::__cxx11::basic_string<char> >, 
std::equal_to<std::__cxx11::basic_string<char> >, std::allocator<std::__cxx11::basic_string<char> >, 
std::deque<std::__cxx11::basic_string<char>, std::allocator<std::__cxx11::basic_string<char> > > > > >::convert(Poco::Int8&) const'
  void convert(Int8&) const
   ^
/export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/Foundation/include/Poco/Dynamic/Struct.h:886:7: error: 'void 
Poco::Dynamic::VarHolderImpl<Poco::Dynamic::Struct<int, tsl::ordered_map<int, Poco::Dynamic::Var, std::hash<int>, std::equal_to<int>, 
std::allocator<std::pair<int, Poco::Dynamic::Var> >, std::deque<std::pair<int, Poco::Dynamic::Var>, std::allocator<std::pair<int, 
Poco::Dynamic::Var> > > >, tsl::ordered_set<int, std::hash<int>, std::equal_to<int>, std::allocator<int>, std::deque<int, 
std::allocator<int> > > > >::convert(char&) const' cannot be overloaded
  void convert(char&) const
   ^
/export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/Foundation/include/Poco/Dynamic/Struct.h:831:7: error: with 
'void Poco::Dynamic::VarHolderImpl<Poco::Dynamic::Struct<int, tsl::ordered_map<int, Poco::Dynamic::Var, std::hash<int>, 
std::equal_to<int>, std::allocator<std::pair<int, Poco::Dynamic::Var> >, std::deque<std::pair<int, Poco::Dynamic::Var>, 
std::allocator<std::pair<int, Poco::Dynamic::Var> > > >, tsl::ordered_set<int, std::hash<int>, std::equal_to<int>, std::allocator<int>, 
std::deque<int, std::allocator<int> > > > >::convert(Poco::Int8&) const'
  void convert(Int8&) const
   ^
gmake[2]: *** [Foundation/CMakeFiles/Foundation.dir/build.make:3663: Foundation/CMakeFiles/Foundation.dir/src/Var.cpp.o] Error 1
gmake[2]: Leaving directory '/export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/cmake-build'
gmake[1]: *** [CMakeFiles/Makefile2:118: Foundation/CMakeFiles/Foundation.dir/all] Error 2
gmake[1]: Leaving directory '/export/home/-/poco/solaris-poco/poco-poco-1.12.2-release/cmake-build'
gmake: *** [Makefile:150: all] Error 2