compiler-rt/test/fuzzer/strncmp.test sometimes fails with runs=10M

[chapuni]

With runs=10M, this test sometimes fails since it doesn't meet BINGO within the run count.
(I saw failures on aarch64-ubuntu20.04 stage2.)
I committed increasing runs=20M in 851817b.
(llvmorg-20-init-8891-g851817b49427)

I don't know its run count would be predicable and proper or not.

It's ok to close this if increasing the count would be appropriate in this case.