ISLzmaDec.obj and ISLzma2Dec.obj are compiled using the
Borland C++Builder 6 compiler ("Borland C++ 5.6.4 for Win32")
as follows:

bcc32 -c -pr -O2 ISLzmaDec.c ISLzma2Dec.c

Add -v if you wish to enable source-level debugging, which
makes it possible to step through the C code from within
Delphi.
