Add function to mix in an additional input into a RAND_POOL #1097

Job	Run time
jitter	6m 4s
run-checker (enable-asan enable-ubsan no-shared no-asm -DOPENSSL_SMALL_FOOTPRINT)	10m 17s
run-checker (no-dso)	5m 18s
run-checker (no-dynamic-engine)	5m 21s
run-checker (no-ec2m enable-fips)	5m 37s
run-checker (no-engine no-shared)	4m 29s
run-checker (no-err)	5m 38s
run-checker (no-filenames)	5m 23s
run-checker (enable-ubsan no-asm -DOPENSSL_SMALL_FOOTPRINT -fno-sanitize=alignment)	8m 6s
run-checker (no-module)	5m 8s
run-checker (no-ocsp)	5m 27s
run-checker (no-pinshared)	5m 25s
run-checker (no-srp)	5m 27s
run-checker (no-srtp)	5m 43s
run-checker (no-ts)	5m 34s
run-checker (no-integrity-only-ciphers)	5m 28s
run-checker (enable-weak-ssl-ciphers)	5m 34s
run-checker (enable-zlib)	5m 22s
run-checker (enable-pie)	5m 29s
	1h 50m 50s

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