The attached patch is against the RexxSQL-2.5.tar.gz source tree. (There doesn't seem to be a cvs repository.)
When applied, RexxSQL can be compiled using ooRexx 4.0.0 as the interpreter.
On Windows use INT=OOREXX4
On a unix-like system using configure use --with-rexx=oorexx4
Tested on both Windows and Linux (Fedora Core 10) using MySQL. simple.cmd and tester.cmd run without errors.