Orange C failed to link on Cygwin

[chatchoi]

It's linking fine on Linux, but failed to link on Cygwin:

g++ -c -D__MSVCRT__ -DHAVE_UNISTD_H=1 -DSQLITE_OS_UNIX -Wno-int-to-pointer-cast -I../util -I../ocpp -I../occ -I../objlib -I../oasm -I../occopt -fpermissive -Dx64 -DUSE_LONGLONG -DGNUC -std=gnu++14 -o /c/OrangeC/src/occopt/obj/gcc-linux/optmain.o optmain.cpp
gcc -L/c/OrangeC/src/../src/lib/gcc-linux -o occopt.exe /c/OrangeC/src/occopt/obj/gcc-linux/optmain.o -Wl,--start-group -loccopt -lutil -locpplib -Wl,--end-group -lstdc++ -lpthread -ldl
/usr/lib/gcc/x86_64-pc-msys/13.3.0/../../../../x86_64-pc-msys/bin/ld: /c/OrangeC/src/../src/lib/gcc-linux/liboccopt.a(iconst.o):iconst.cpp:(.text+0x5b4a): undefined reference to `Optimizer::RemoveInstruction(Optimizer::quad_t*)'
collect2: error: ld returned 1 exit status