Linux has an equivalent feature available through the "auxiliary vector," a set of data passed as the secret fourth parameter to main() / on the stack at program startup (after the secret third parameter, envp). http://man7.org/linux/man-pages/man3/getauxval.3.html and https://lwn.net/Articles/519085/ have a description of the auxiliary vector. One key, AT_RANDOM, contains 16 bytes (128 bits) of random data which libc uses for stack protector cookies. glibc uses this to implement stack and pointer protector cookies.

(Unfortunately, glibc uses this data directly as stack and pointer protector cookies, instead of deriving something from it, which means it feels a little risky to use this to initialize a userspace PRNG. I guess you shouldn't be leaking cookies....)

Linux added this in v2.6.29 (2009) in https://github.com/torvalds/linux/commit/f06295b4 , and glibc in 2009 added support for using it if available to set up cookies (it previously read from /dev/urandom). That said, I don't really think the "we're the only OS" game is a game worth playing - if it's a security improvement, it's best if everyone has it, regardless of OS!