Add additional EVP_SKEY helpers #529

Job	Run time
jitter	6m 3s
run-checker (enable-asan enable-ubsan no-shared no-asm -DOPENSSL_SMALL_FOOTPRINT -fno-sanitize=fu...	11m 22s
run-checker (no-dso)	5m 28s
run-checker (no-dynamic-engine)	6m 22s
run-checker (no-ec2m enable-fips)	6m 14s
run-checker (no-engine no-shared)	4m 27s
run-checker (no-err)	5m 37s
run-checker (no-filenames)	5m 35s
run-checker (enable-ubsan no-asm -DOPENSSL_SMALL_FOOTPRINT -fno-sanitize=function)	8m 41s
run-checker (no-module)	5m 29s
run-checker (no-ocsp)	5m 35s
run-checker (no-pinshared)	5m 31s
run-checker (no-srp)	5m 36s
run-checker (no-srtp)	5m 41s
run-checker (no-ts)	5m 31s
run-checker (no-integrity-only-ciphers)	5m 28s
run-checker (enable-weak-ssl-ciphers)	5m 44s
run-checker (enable-zlib)	5m 31s
run-checker (enable-pie)	5m 35s
	1h 55m 30s

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