The compiler has experimental MIPS64EL support, you'll probably have to cross compile however as I think the mips-linux distribution we provide as download is not the little endian one.
Assuming you have the correct binutils it should essentially be enough to do the following in a source distribution of FPC:
make all OS_TARGET=linux CPU_TARGET=mipsel BINUTILSPREFIX=mipsel-linux-gnu- FPMAKEOPT="-T <cores>" -j <cores>
make install OS_TARGET=linux CPU_TARGET=mipsel INSTALL_PREFIX=/where/you/want/your/compiler
The <cores> is the number of CPU cores you have and the prefix needs to match the one of your binutils.