Just checked, getrandom.c is in build_dir/toolchain-mips_24kc_gcc-8.4.0_musl/musl-1.1.24/src/linux. It is downloaded so it appears only after a make. The 902-xxx pacth is redondant, don't use it in this version (and delete it if it is present).
2) the folder where it resides, for me rutos-ath79-trb2-gpl