gcc error while building on arch linux

[iitalics]

Trying to build a project that uses openssl gives an error when compiling some C code:

error: failed to run custom build command for `openssl v0.7.14`
process didn't exit successfully: `/home/milo/Git/project/target/debug/build/openssl-7c908dc9909f2047/build-script-build` (exit code: 101)
--- stdout
TARGET = Some("x86_64-unknown-linux-gnu")
OPT_LEVEL = Some("0")
TARGET = Some("x86_64-unknown-linux-gnu")
HOST = Some("x86_64-unknown-linux-gnu")
TARGET = Some("x86_64-unknown-linux-gnu")
TARGET = Some("x86_64-unknown-linux-gnu")
HOST = Some("x86_64-unknown-linux-gnu")
CC_x86_64-unknown-linux-gnu = None
CC_x86_64_unknown_linux_gnu = None
HOST_CC = None
CC = None
HOST = Some("x86_64-unknown-linux-gnu")
TARGET = Some("x86_64-unknown-linux-gnu")
HOST = Some("x86_64-unknown-linux-gnu")
CFLAGS_x86_64-unknown-linux-gnu = None
CFLAGS_x86_64_unknown_linux_gnu = None
HOST_CFLAGS = None
CFLAGS = None
DEBUG = Some("true")
running: "cc" "-O0" "-ffunction-sections" "-fdata-sections" "-fPIC" "-g" "-m64" "-Wall" "-Wextra" "-o" "/home/milo/Git/project/target/debug/build/openssl-c0b8832924485c23/out/src/c_helpers.o" "-c" "src/c_helpers.c"
cargo:warning=src/c_helpers.c: In function ‘rust_SSL_clone’:
cargo:warning=src/c_helpers.c:4:5: warning: implicit declaration of function ‘CRYPTO_add’; did you mean ‘CRYPTO_free’? [-Wimplicit-function-declaration]
cargo:warning=     CRYPTO_add(&ssl->references, 1, CRYPTO_LOCK_SSL);
cargo:warning=     ^~~~~~~~~~
cargo:warning=     CRYPTO_free
cargo:warning=src/c_helpers.c:4:20: error: dereferencing pointer to incomplete type ‘SSL {aka struct ssl_st}’
cargo:warning=     CRYPTO_add(&ssl->references, 1, CRYPTO_LOCK_SSL);
cargo:warning=                    ^~
cargo:warning=src/c_helpers.c:4:37: error: ‘CRYPTO_LOCK_SSL’ undeclared (first use in this function); did you mean ‘CRYPTO_LOCK’?
cargo:warning=     CRYPTO_add(&ssl->references, 1, CRYPTO_LOCK_SSL);
cargo:warning=                                     ^~~~~~~~~~~~~~~
cargo:warning=                                     CRYPTO_LOCK
cargo:warning=src/c_helpers.c:4:37: note: each undeclared identifier is reported only once for each function it appears in
cargo:warning=src/c_helpers.c: In function ‘rust_SSL_CTX_clone’:
cargo:warning=src/c_helpers.c:8:20: error: dereferencing pointer to incomplete type ‘SSL_CTX {aka struct ssl_ctx_st}’
cargo:warning=     CRYPTO_add(&ctx->references,1,CRYPTO_LOCK_SSL_CTX);
cargo:warning=                    ^~
cargo:warning=src/c_helpers.c:8:35: error: ‘CRYPTO_LOCK_SSL_CTX’ undeclared (first use in this function); did you mean ‘CRYPTO_EX_INDEX_SSL_CTX’?
cargo:warning=     CRYPTO_add(&ctx->references,1,CRYPTO_LOCK_SSL_CTX);
cargo:warning=                                   ^~~~~~~~~~~~~~~~~~~
cargo:warning=                                   CRYPTO_EX_INDEX_SSL_CTX
cargo:warning=src/c_helpers.c: In function ‘rust_X509_clone’:
cargo:warning=src/c_helpers.c:12:21: error: dereferencing pointer to incomplete type ‘X509 {aka struct x509_st}’
cargo:warning=     CRYPTO_add(&x509->references,1,CRYPTO_LOCK_X509);
cargo:warning=                     ^~
cargo:warning=src/c_helpers.c:12:36: error: ‘CRYPTO_LOCK_X509’ undeclared (first use in this function); did you mean ‘CRYPTO_LOCK’?
cargo:warning=     CRYPTO_add(&x509->references,1,CRYPTO_LOCK_X509);
cargo:warning=                                    ^~~~~~~~~~~~~~~~
cargo:warning=                                    CRYPTO_LOCK
exit code: 1

System is up-to-date Arch Linux

• Linux 4.12.10
• openssl 1.1.0.f-2
• gcc 7.2.0
• rust 1.20.0 stable