The source code for the RLARM libs can be got by editting the link you were given, changing the 0 to a 1. (eg 4.20 to 4.21)
Enter your PIC/LIC and down load the source code.
New version broke my projects requires a change of fileconfig.c to fix
Source files havent been updated from 4.2 to 4.21 in comments though, so make sure you have a back up of previous versions.
The error was related to not being able to find a #define used in the FS code.
The link is fine for the tool and IDE but versions later than I think 4.14 of RL ARM lib, I had to sign a NDA with ARM to get hold of the source code. Otherwise I belive its just precompiled Libs.