filezilla=3.20.0 build failed

gistfile1.txt

g++ -DHAVE_CONFIG_H -I. -I../../src/include  -I./../include -I/usr/local/include -I/usr/include/p11-kit-1 -I/usr/lib/x86_64-linux-gnu/wx/include/gtk2-unicode-3.0 -I/usr/include/wx-3.0 -D_FILE_OFFSET_BITS=64 -DWXUSINGDLL -D__WXGTK__ -fpch-preprocess  -g -O2 -Wall -g -std=gnu++14 -MT libengine_a-sftpcontrolsocket.o -MD -MP -MF .deps/libengine_a-sftpcontrolsocket.Tpo -c -o libengine_a-sftpcontrolsocket.o `test -f 'sftpcontrolsocket.cpp' || echo './'`sftpcontrolsocket.cpp
sftpcontrolsocket.cpp: In member function ‘std::__cxx11::wstring CSftpControlSocket::QuoteFilename(const wstring&)’:
sftpcontrolsocket.cpp:2034:64: error: binding ‘const wstring {aka const std::__cxx11::basic_string<wchar_t>}’ to reference of type ‘std::__cxx11::wstring& {aka std::__cxx11::basic_string<wchar_t>&}’ discards qualifiers
  return L"\"" + fz::replace_substrings(filename, L"\"", L"\"\"") + L"\"";
                                                                ^
In file included from /usr/local/include/libfilezilla/libfilezilla.hpp:7:0,
                 from ../../src/include/libfilezilla_engine.h:35,
                 from filezilla.h:1:
/usr/local/include/libfilezilla/string.hpp:259:23: note:   initializing argument 1 of ‘void fz::replace_substrings(std::__cxx11::wstring&, const wstring&, const wstring&)’
 void FZ_PUBLIC_SYMBOL replace_substrings(std::wstring& in, std::wstring const& find, std::wstring const& replacement);
                       ^
Makefile:920: recipe for target 'libengine_a-sftpcontrolsocket.o' failed
make[3]: *** [libengine_a-sftpcontrolsocket.o] Error 1
make[3]: Leaving directory '/home/d9k/inst/filezilla/manually/filezilla-3.20.0/src/engine'
Makefile:454: recipe for target 'all' failed
make[2]: *** [all] Error 2
make[2]: Leaving directory '/home/d9k/inst/filezilla/manually/filezilla-3.20.0/src/engine'
Makefile:424: recipe for target 'all-recursive' failed
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory '/home/d9k/inst/filezilla/manually/filezilla-3.20.0/src'
Makefile:608: recipe for target 'all-recursive' failed
make: *** [all-recursive] Error 1