From the Makefile included in the sllogiclogger.2012-12-24.tar.gz archive it seems to be gcc.
Please read the Makefile header and you will also have the links to the tools used.
I can confirm that I have used a newer version of the GCC toolchain recommended there
to compile the project under MinGW Windows (just a bit more dificult than Linux)
and with minimal modifications for the Stellarisware and the flasher paths in the makefile it built ok.
tkg