1) Download the InnoSetup source https://github.com/jrsoftware/issrc
   and copy its Projects\Lzma2\Decoder and Projects\Lzma\C directories to the Src directory
2) Compile Win32 version of Decoder:
   bcc32 -c -pr -O2 ISLzmaDec.c ISLzma2Dec.c
   and move the .obj files to win32
3) Compile Win64 version of Decoder:
   bcc64 -c ISLzmaDec.c ISLzma2Dec.c
   and move the .o files to win64
