コメントありがとうございます。

今回、方針を決めており、PHP本体は最小構成 (--apxs2 --enable-debug) でビルドし、後からphpizeでphp-src/ext配下の拡張機能を必要なタイミングで個別にインストールしています。--with-xxxでPHPソースコードビルド時に有効にするのは、汎用性が低いためです。

OpenSSLは1.1.1aをソースコードからビルド済みで、これを使ってPHPの拡張機能のビルドを試しています。
ビルドはできるのですが、make testで失敗が報告されてしまいます。

具体的には、少々長いですが以下です。テスト失敗を無視してmake installするという手もありますが、これは最後の手段にします。
時間がかかりますが、失敗したテストケースを個別に実行するなどして、引き続き原因を調査します。

=====================================================================
FAILED TEST SUMMARY
---------------------------------------------------------------------
#46127 php_openssl_tcp_sockop_accept forgets to set context on accepted stream [tests/bug46127.phpt]
Bug #48182: ssl handshake fails during asynchronous socket connection [tests/bug48182.phpt]
Bug #54992: Stream not closed and error not returned when SSL CN_match fails [tests/bug54992.phpt]
Bug #65538: SSL context "cafile" supports stream wrappers [tests/bug65538_001.phpt]
Bug #65538: SSL context "cafile" disallows URL stream wrappers [tests/bug65538_002.phpt]
Bug #65538: SSL context "cafile" supports phar wrapper [tests/bug65538_003.phpt]
Bug #65729: CN_match gives false positive when wildcard is used [tests/bug65729.phpt]
Bug #68265: SAN match fails with trailing DNS dot [tests/bug68265.phpt]
Bug #68879: Match IP address fields in subjectAltName checks [tests/bug68879.phpt]
Bug #68920: peer_fingerprint input checks should be strict [tests/bug68920.phpt]
Bug #69215: Crypto servers should send client CA list [tests/bug69215.phpt]
Bug #72333: fwrite() on non-blocking SSL sockets doesn't work [tests/bug72333.phpt]
Bug #74159: Writing a large buffer to non-blocking encrypted streams fails [tests/bug74159.phpt]
Bug #76705: unusable ssl => peer_fingerprint in stream_context_create() [tests/bug76705.phpt]
Bug #76705: feof might hang on TLS streams in case of fragmented TLS records [tests/bug77390.phpt]
capture_peer_cert context captures on verify failure [tests/capture_peer_cert_001.phpt]
Testing peer fingerprint on connection [tests/openssl_peer_fingerprint_basic.phpt]
Peer verification enabled for client streams [tests/peer_verification.phpt]
Peer verification matches SAN names [tests/san_peer_matching.phpt]
Capture SSL session meta array in stream context [tests/session_meta_capture.phpt]
sni_server [tests/sni_server.phpt]
sni_server with separate pk and cert [tests/sni_server_key_cert.phpt]
Basic bitwise stream crypto context flag assignment [tests/stream_crypto_flags_001.phpt]
TLSv1.1 and TLSv1.2 bitwise stream crypto flag assignment [tests/stream_crypto_flags_002.phpt]
Server bitwise stream crypto flag assignment [tests/stream_crypto_flags_003.phpt]
Specific protocol method specification [tests/stream_crypto_flags_004.phpt]
security_level setting to prohibit cert [tests/stream_security_level.phpt]
Verify host name by default in client transfers [tests/stream_verify_peer_name_001.phpt]
Allow host name mismatch when "verify_host" disabled [tests/stream_verify_peer_name_002.phpt]
Host name mismatch triggers error [tests/stream_verify_peer_name_003.phpt]
Specific crypto method for ssl:// transports. [tests/streams_crypto_method.phpt]
tls stream wrapper with min version 1.0 and max version 1.1 [tests/tls_min_v1.0_max_v1.1_wrapper.phpt]
tls stream wrapper [tests/tls_wrapper.phpt]
tlsv1.0 stream wrapper [tests/tlsv1.0_wrapper.phpt]
tlsv1.1 stream wrapper [tests/tlsv1.1_wrapper.phpt]
tlsv1.2 stream wrapper [tests/tlsv1.2_wrapper.phpt]
=====================================================================