Fix data race between SSL_SESSION_list_add and ssl_session_dup #24

Job	Run time
run-checker (enable-asan enable-ubsan no-shared no-asm -DOPENSSL_SMALL_FOOTPRINT)	6s
run-checker (no-ct)	4s
run-checker (no-dso)	7s
run-checker (no-dynamic-engine)	3s
run-checker (no-ec2m)	7s
run-checker (no-engine no-shared)	6s
run-checker (no-err)	6s
run-checker (no-filenames)	6s
run-checker (enable-ubsan no-asm -DOPENSSL_SMALL_FOOTPRINT -fno-sanitize=alignment)	6s
run-checker (no-module)	7s
run-checker (no-ocsp)	6s
run-checker (no-pinshared)	6s
run-checker (no-srp)	6s
run-checker (no-srtp)	7s
run-checker (no-ts)	6s
run-checker (enable-weak-ssl-ciphers)	4s
run-checker (enable-zlib)	6s
	1m 39s

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