-Wstrict-aliasing warnings

[phlptp]

There are some strict-aliasing warnings in later Gcc versions that should be fixed.

In file included from /home/travis/build/GMLC-TDC/HELICS/ThirdParty/units/units/unit_definitions.hpp:9:0,
                 from /home/travis/build/GMLC-TDC/HELICS/ThirdParty/units/units/units.hpp:8,
                 from /home/travis/build/GMLC-TDC/HELICS/ThirdParty/units/units/units.cpp:7:
/home/travis/build/GMLC-TDC/HELICS/ThirdParty/units/units/units_decl.hpp: In member function ‘std::size_t std::hash<units::detail::unit_data>::operator()(const units::detail::unit_data&) const’:
/home/travis/build/GMLC-TDC/HELICS/ThirdParty/units/units/units_decl.hpp:315:78: warning: dereferencing type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]
         return hash<unsigned int>()(*reinterpret_cast<const unsigned int*>(&x));
                                                                              ^
[  3%] Building CXX object ThirdParty/utilities/gmlc/utilities/CMakeFiles/gmlc_utilities.dir/charMapper.cpp.o
[  3%] Building CXX object ThirdParty/jsoncpp/src/lib_json/CMakeFiles/jsoncpp_lib.dir/json_value.cpp.o
[  3%] Building CXX object ThirdParty/utilities/gmlc/utilities/CMakeFiles/gmlc_utilities.dir/string_viewOps.cpp.o
[  4%] Building CXX object ThirdParty/units/units/CMakeFiles/units-static.dir/x12_conv.cpp.o
[  4%] Building CXX object ThirdParty/fmtlib/CMakeFiles/fmt.dir/src/posix.cc.o
[  4%] Building CXX object ThirdParty/utilities/gmlc/utilities/CMakeFiles/gmlc_utilities.dir/stringOps.cpp.o
In file included from /home/travis/build/GMLC-TDC/HELICS/ThirdParty/units/units/unit_definitions.hpp:9:0,
                 from /home/travis/build/GMLC-TDC/HELICS/ThirdParty/units/units/units.hpp:8,
                 from /home/travis/build/GMLC-TDC/HELICS/ThirdParty/units/units/x12_conv.cpp:7:
/home/travis/build/GMLC-TDC/HELICS/ThirdParty/units/units/units_decl.hpp: In member function ‘std::size_t std::hash<units::detail::unit_data>::operator()(const units::detail::unit_data&) const’:
/home/travis/build/GMLC-TDC/HELICS/ThirdParty/units/units/units_decl.hpp:315:78: warning: dereferencing type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]
         return hash<unsigned int>()(*reinterpret_cast<const unsigned int*>(&x));
                                                                              ^
[  4%] Building CXX object ThirdParty/jsoncpp/src/lib_json/CMakeFiles/jsoncpp_lib.dir/json_writer.cpp.o

the warning should be added to compilation and the warnings fixed.

[phlptp]

This appears to only show up on GCC 6