This is defeatist: compilers do not usually use the system RNG to make decisions, so what's happening is entirely accidental introduction of difference which propagates.

There is "intentional input" (contents of the source files), and "accidental input" (source file full paths, timestamps, layout of memory given to you by the OS, and so on). A reproducible build system should give the same output for the same "intentional input".

(the only place where you do see RNG driven optimization is things like FPGA routing, which is a mess of closed toolchains anyway. It has no place in regular software compilers.)