Unexpected compilation error "/bin/sh: 1: Illegal number: "

when my makefile run in the shared Runner supplied by GitLab, the following issue occurs

/bin/sh: 1: /builds/iottask/anderson_router_platform/toolchain/buildroot-gcc342/bin/mipsel-linux-as: not found
/bin/sh: 1: [: Illegal number:

off course, there is such file - mipsel-linux-as in that path.

could anybody give some direction about this issue?