x509_vfy.c and x509_lu.c: refactor find_issuer(), X509_STORE_CTX_get1… #1524

Job	Run time
run-checker (no-cmp)	5m 0s
run-checker (no-cms)	5m 11s
run-checker (no-dgram)	4m 55s
run-checker (no-dh)	5m 19s
run-checker (no-dtls)	5m 13s
run-checker (no-ec)	4m 33s
run-checker (no-ecx)	5m 20s
run-checker (no-http)	5m 9s
run-checker (no-legacy)	5m 17s
run-checker (no-sock)	4m 39s
run-checker (enable-ssl-trace)	5m 25s
run-checker (no-stdio)	2m 15s
run-checker (no-threads)	5m 15s
run-checker (no-thread-pool)	5m 19s
run-checker (no-default-thread-pool)	5m 18s
run-checker (no-tls)	4m 52s
run-checker (no-tls1_2)	5m 8s
run-checker (no-tls1_3)	4m 57s
run-checker (enable-trace enable-fips)	5m 46s
run-checker (no-ui)	5m 29s
run-checker (no-quic)	5m 3s
	1h 45m 23s

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