Dereferencing pointer to incomplete type in openssl_shim.c

Job #2527669 failed for 0a19bb3b:

/bin/bash ../../libtool  --tag=CC   --mode=compile gcc -DHAVE_CONFIG_H -I. -I../..  -D_FORTIFY_SOURCE=2 -DISC_MEM_DEFAULTFILL=1 -DISC_MEM_TRACKLINES=1 -DISC_LIST_CHECKINIT=1 -DISC_STATS_CHECKUNDERFLOW=1 -include ../../config.h -I./include -I../../include -I../../lib/isc/include -I../../lib/isc/include     -I/usr/include/json-c  -I/usr/include/libxml2  -Wall -Wextra -Wwrite-strings -Wpointer-arith -Wno-missing-field-initializers -Wformat -Wshadow -Werror=implicit-function-declaration -Werror=missing-prototypes -Werror=format-security -Werror=parentheses -Werror=implicit -Werror=strict-prototypes -Werror=vla -fno-strict-aliasing -fno-delete-null-pointer-checks -fdiagnostics-show-option -Werror -fno-omit-frame-pointer -fno-optimize-sibling-calls -O1 -g -Wall -Wextra -O2 -pthread -MT libisc_la-random.lo -MD -MP -MF .deps/libisc_la-random.Tpo -c -o libisc_la-random.lo `test -f 'random.c' || echo './'`random.c
openssl_shim.c: In function 'SSL_SESSION_is_resumable':
openssl_shim.c:203:15: error: dereferencing pointer to incomplete type 'SSL_SESSION {aka const struct ssl_session_st}'
  return (!sess->not_resumable &&
               ^~
openssl_shim.c:205:1: error: control reaches end of non-void function [-Werror=return-type]
 }
 ^
cc1: all warnings being treated as errors

The culprit seems to be in 35338b41 and only on Debian 9 "stretch".