Support MIPS little-endian targets #72
Description
Currently when cross-compiling for MIPS the only supported prefix is the one for big-endian targets (mips-unknown-linux-gnu), little-endian targets have their own prefix that should be added to the supported prefix list (mipsel-unknown-linux-gnu).
Also, using an unsupported prefix silently uses the host compiler which doesn't seem like sane behaviour since it will cause objects in a project to be compiled for the wrong target.