This is a replay of CL 516859, after its rollback in CL 543895,
with big-endian systems fixed and the tests disabled on RISC-V
since the compiler is broken there (#64285).
ChaCha8 provides a cryptographically strong generator
alongside PCG, so that people who want stronger randomness
have access to that. On systems with 128-bit vector math
assembly (amd64 and arm64), ChaCha8 runs at about the same
speed as PCG (25% slower on amd64, 2% faster on arm64).
Fixes #64284.
Change-Id: I6290bb8ace28e1aff9a61f805dbe380ccdf25b94
Reviewed-on: https://go-review.googlesource.com/c/go/+/546020 Reviewed-by: Filippo Valsorda <filippo@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>