winbuilder compiler warnings

[RobinHankin]

d:/Compiler/rtools40/mingw32/bin/g++  -std=gnu++11 -I"D:/RCompile/recent/R-4.0.5/include" -DNDEBUG  -I'd:/RCompile/CRANpkg/lib/4.0/Rcpp/include'   -I"d:/Compiler/gcc-4.9.3/local330/include"     -O2 -Wall  -mfpmath=sse -msse2 -mstackrealign -c RcppExports.cpp -o RcppExports.o
d:/Compiler/rtools40/mingw32/bin/g++  -std=gnu++11 -I"D:/RCompile/recent/R-4.0.5/include" -DNDEBUG  -I'd:/RCompile/CRANpkg/lib/4.0/Rcpp/include'   -I"d:/Compiler/gcc-4.9.3/local330/include"     -O2 -Wall  -mfpmath=sse -msse2 -mstackrealign -c free.cpp -o free.o
free.cpp: In function 'freealg prepare(Rcpp::List, Rcpp::NumericVector)':
free.cpp:76:33: warning: comparison of integer expressions of different signedness: 'unsigned int' and 'R_xlen_t' {aka 'int'} [-Wsign-compare]
         for(unsigned int j=0 ; j<words.size() ; ++j){
                                ~^~~~~~~~~~~~~
free.cpp: In function 'freealg diff1(freealg, unsigned int)':
free.cpp:140:23: warning: comparison of integer expressions of different signedness: 'int' and 'const unsigned int' [-Wsign-compare]
             if( (*iw) == r){         // differential matches symbol, same sign
                 ~~~~~~^~~~
free.cpp:148:23: warning: comparison of integer expressions of different signedness: 'int' and 'unsigned int' [-Wsign-compare]
             if( (*iw) == -r){    // ... so now search for an opposite sign match
                 ~~~~~~^~~~~
free.cpp: In function 'freealg diffn(freealg, Rcpp::NumericVector)':
free.cpp:167:29: warning: comparison of integer expressions of different signedness: 'unsigned int' and 'R_xlen_t' {aka 'int'} [-Wsign-compare]
     for(unsigned int i=0 ; i<r.size() ; ++i){
                            ~^~~~~~~~~
d:/Compiler/rtools40/mingw32/bin/g++ -shared -s -static-libgcc -o freealg.dll tmp.def RcppExports.o free.o -Ld:/Compiler/gcc-4.9.3/local330/lib/i386 -Ld:/Compiler/gcc-4.9.3/local330/lib -LD:/RCompile/recent/R-4.0.5/bin/i386 -lR
installing to d:/RCompile/CRANguest/R-release/lib/00LOCK-freealg/00new/freealg/libs/i386

*** arch - x64
d:/Compiler/rtools40/mingw64/bin/g++  -std=gnu++11 -I"D:/RCompile/recent/R-4.0.5/include" -DNDEBUG  -I'd:/RCompile/CRANpkg/lib/4.0/Rcpp/include'   -I"d:/Compiler/gcc-4.9.3/local330/include"     -O2 -Wall  -mfpmath=sse -msse2 -mstackrealign -c RcppExports.cpp -o RcppExports.o
d:/Compiler/rtools40/mingw64/bin/g++  -std=gnu++11 -I"D:/RCompile/recent/R-4.0.5/include" -DNDEBUG  -I'd:/RCompile/CRANpkg/lib/4.0/Rcpp/include'   -I"d:/Compiler/gcc-4.9.3/local330/include"     -O2 -Wall  -mfpmath=sse -msse2 -mstackrealign -c free.cpp -o free.o
free.cpp: In function 'freealg diff1(freealg, unsigned int)':
free.cpp:140:23: warning: comparison of integer expressions of different signedness: 'int' and 'const unsigned int' [-Wsign-compare]
             if( (*iw) == r){         // differential matches symbol, same sign
                 ~~~~~~^~~~
free.cpp:148:23: warning: comparison of integer expressions of different signedness: 'int' and 'unsigned int' [-Wsign-compare]
             if( (*iw) == -r){    // ... so now search for an opposite sign match
                 ~~~~~~^~~~~
d:/Compiler/rtools40/mingw64/bin/g++ -shared -s -static-libgcc -o freealg.dll tmp.def RcppExports.o free.o -Ld:/Compiler/gcc-4.9.3/local330/lib/x64 -Ld:/Compiler/gcc-4.9.3/local330/lib -LD:/RCompile/recent/R-4.0.5/bin/x64 -lR
installing to d:/RCompile/CRANguest/R-release/lib/00LOCK-freealg/00new/freealg/libs/x64
** R