Build failed (to run custom build command)

Nobody has claimed this yet.

Commit b33c498e99883536519bc01f19d2c6b081eebae1, on Ubuntu 20.04. This is the log:

```
$ cargo build --release
Updating crates.io index
Updating git repository `https://github.com/matrix-org/rust-matrix-state-map`
Downloaded ansi_term v0.11.0
Downloaded memoffset v0.6.1
Downloaded opaque-debug v0.3.0
Downloaded phf_shared v0.8.0
Downloaded openssl-sys v0.9.61
Downloaded parking_lot_core v0.8.3
Downloaded rayon v1.5.0
Downloaded sha2 v0.9.3
Downloaded scopeguard v1.1.0
Downloaded strsim v0.8.0
Downloaded slab v0.4.2
Downloaded subtle v2.4.0
Downloaded string_cache v0.8.1
Downloaded vec_map v0.8.2
Downloaded terminal_size v0.1.16
Downloaded socket2 v0.3.19
Downloaded smallvec v1.6.1
Downloaded rayon-core v1.9.0
Downloaded unicode-xid v0.2.1
Downloaded cfg-if v1.0.0
Downloaded byteorder v1.4.3
Downloaded block-buffer v0.9.0
Downloaded syn v1.0.64
Downloaded tokio-util v0.6.4
Downloaded crypto-mac v0.10.0
Downloaded cpuid-bool v0.1.2
Downloaded console v0.14.1
Downloaded postgres v0.19.0
Downloaded number_prefix v0.3.0
Downloaded postgres-openssl v0.5.0
Downloaded crossbeam-channel v0.5.0
Downloaded bitflags v1.2.1
Downloaded async-trait v0.1.48
Downloaded cc v1.0.67
Downloaded futures-channel v0.3.13
Downloaded hmac v0.10.1
Downloaded memchr v2.3.4
Downloaded indicatif v0.15.0
Downloaded generic-array v0.14.4
Downloaded futures-util v0.3.13
Downloaded num_cpus v1.13.0
Downloaded once_cell v1.7.2
Downloaded precomputed-hash v0.1.1
Downloaded version_check v0.9.3
Downloaded rand_core v0.6.2
Downloaded futures-macro v0.3.13
Downloaded foreign-types v0.3.2
Downloaded pin-utils v0.1.0
Downloaded parking_lot v0.11.1
Downloaded siphasher v0.3.3
Downloaded futures-executor v0.3.13
Downloaded log v0.4.14
Downloaded lock_api v0.4.2
Downloaded tokio v1.3.0
Downloaded libc v0.2.90
Downloaded getrandom v0.2.2
Downloaded futures-task v0.3.13
Downloaded crossbeam-utils v0.8.3
Downloaded postgres-protocol v0.6.0
Downloaded proc-macro-hack v0.5.19
Downloaded openssl v0.10.33
Downloaded pin-project-internal v1.0.5
Downloaded ppv-lite86 v0.2.10
Downloaded unicode-bidi v0.3.4
Downloaded tinyvec v1.1.1
Downloaded stringprep v0.1.2
Downloaded regex-syntax v0.6.23
Downloaded pkg-config v0.3.19
Downloaded pin-project-lite v0.2.6
Downloaded mio v0.7.10
Downloaded tokio-postgres v0.7.0
Downloaded unicode-width v0.1.8
Downloaded typenum v1.13.0
Downloaded crossbeam-deque v0.8.0
Downloaded proc-macro-nested v0.1.7
Downloaded tokio-openssl v0.6.1
Downloaded fs_extra v1.2.0
Downloaded quote v1.0.9
Downloaded matches v0.1.8
Downloaded autocfg v1.0.1
Downloaded md5 v0.7.0
Downloaded atty v0.2.14
Downloaded unicode-normalization v0.1.17
Downloaded base64 v0.13.0
Downloaded tinyvec_macros v0.1.0
Downloaded regex v1.4.5
Downloaded serde v1.0.124
Downloaded textwrap v0.11.0
Downloaded proc-macro2 v1.0.24
Downloaded jemalloc-sys v0.3.2
Downloaded pin-project v1.0.5
Downloaded futures-io v0.3.13
Downloaded phf v0.8.0
Downloaded percent-encoding v2.1.0
Downloaded instant v0.1.9
Downloaded either v1.6.1
Downloaded crossbeam-epoch v0.9.3
Downloaded foreign-types-shared v0.1.1
Downloaded jemallocator v0.3.2
Downloaded new_debug_unreachable v1.0.4
Downloaded lazy_static v1.4.0
Downloaded futures-sink v0.3.13
Downloaded futures-core v0.3.13
Downloaded futures v0.3.13
Downloaded fallible-iterator v0.2.0
Downloaded digest v0.9.0
Downloaded bytes v1.0.1
Downloaded clap v2.33.3
Downloaded rand v0.8.3
Downloaded postgres-types v0.2.0
Downloaded rand_chacha v0.3.0
Downloaded 111 crates (6.2 MB) in 1.09s (largest was `jemalloc-sys` at 1.3 MB)
Compiling libc v0.2.90
Compiling cfg-if v1.0.0
Compiling autocfg v1.0.1
Compiling proc-macro2 v1.0.24
Compiling unicode-xid v0.2.1
Compiling version_check v0.9.3
Compiling typenum v1.13.0
Compiling syn v1.0.64
Compiling memchr v2.3.4
Compiling cc v1.0.67
Compiling proc-macro-hack v0.5.19
Compiling getrandom v0.2.2
Compiling pin-project-lite v0.2.6
Compiling log v0.4.14
Compiling proc-macro-nested v0.1.7
Compiling futures-sink v0.3.13
Compiling lazy_static v1.4.0
Compiling scopeguard v1.1.0
Compiling futures-core v0.3.13
Compiling tinyvec_macros v0.1.0
Compiling bytes v1.0.1
Compiling slab v0.4.2
Compiling matches v0.1.8
Compiling ppv-lite86 v0.2.10
Compiling subtle v2.4.0
Compiling pkg-config v0.3.19
Compiling futures-task v0.3.13
Compiling futures-io v0.3.13
Compiling pin-utils v0.1.0
Compiling cpuid-bool v0.1.2
Compiling bitflags v1.2.1
Compiling siphasher v0.3.3
Compiling opaque-debug v0.3.0
Compiling base64 v0.13.0
Compiling smallvec v1.6.1
Compiling async-trait v0.1.48
Compiling fallible-iterator v0.2.0
Compiling md5 v0.7.0
Compiling byteorder v1.4.3
Compiling unicode-width v0.1.8
Compiling foreign-types-shared v0.1.1
Compiling openssl v0.10.33
Compiling rayon-core v1.9.0
Compiling fs_extra v1.2.0
Compiling percent-encoding v2.1.0
Compiling serde v1.0.124
Compiling once_cell v1.7.2
Compiling regex-syntax v0.6.23
Compiling either v1.6.1
Compiling vec_map v0.8.2
Compiling number_prefix v0.3.0
Compiling strsim v0.8.0
Compiling ansi_term v0.11.0
Compiling new_debug_unreachable v1.0.4
Compiling precomputed-hash v0.1.1
Compiling state-map v0.1.0 (https://github.com/matrix-org/rust-matrix-state-map#211343e8)
Compiling instant v0.1.9
Compiling crossbeam-utils v0.8.3
Compiling tokio v1.3.0
Compiling memoffset v0.6.1
Compiling rayon v1.5.0
Compiling generic-array v0.14.4
Compiling lock_api v0.4.2
Compiling tinyvec v1.1.1
Compiling futures-channel v0.3.13
Compiling unicode-bidi v0.3.4
Compiling phf_shared v0.8.0
Compiling foreign-types v0.3.2
Compiling textwrap v0.11.0
Compiling regex v1.4.5
Compiling openssl-sys v0.9.61
Compiling jemalloc-sys v0.3.2
Compiling phf v0.8.0
Compiling unicode-normalization v0.1.17
Compiling quote v1.0.9
Compiling parking_lot_core v0.8.3
Compiling socket2 v0.3.19
Compiling terminal_size v0.1.16
Compiling num_cpus v1.13.0
Compiling atty v0.2.14
Compiling mio v0.7.10
error: failed to run custom build command for `openssl-sys v0.9.61`

Caused by:
process didn't exit successfully: `/home/xxx/dev/workspace/synapse-compress-state/target/release/build/openssl-sys-c8cca5790468254c/build-script-main` (exit code: 101)
--- stdout
cargo:rustc-cfg=const_fn
cargo:rerun-if-env-changed=X86_64_UNKNOWN_LINUX_GNU_OPENSSL_LIB_DIR
X86_64_UNKNOWN_LINUX_GNU_OPENSSL_LIB_DIR unset
cargo:rerun-if-env-changed=OPENSSL_LIB_DIR
OPENSSL_LIB_DIR unset
cargo:rerun-if-env-changed=X86_64_UNKNOWN_LINUX_GNU_OPENSSL_INCLUDE_DIR
X86_64_UNKNOWN_LINUX_GNU_OPENSSL_INCLUDE_DIR unset
cargo:rerun-if-env-changed=OPENSSL_INCLUDE_DIR
OPENSSL_INCLUDE_DIR unset
cargo:rerun-if-env-changed=X86_64_UNKNOWN_LINUX_GNU_OPENSSL_DIR
X86_64_UNKNOWN_LINUX_GNU_OPENSSL_DIR unset
cargo:rerun-if-env-changed=OPENSSL_DIR
OPENSSL_DIR unset
cargo:rerun-if-env-changed=OPENSSL_NO_PKG_CONFIG
cargo:rerun-if-env-changed=PKG_CONFIG
cargo:rerun-if-env-changed=OPENSSL_STATIC
cargo:rerun-if-env-changed=OPENSSL_DYNAMIC
cargo:rerun-if-env-changed=PKG_CONFIG_ALL_STATIC
cargo:rerun-if-env-changed=PKG_CONFIG_ALL_DYNAMIC
cargo:rerun-if-env-changed=PKG_CONFIG_PATH_x86_64-unknown-linux-gnu
cargo:rerun-if-env-changed=PKG_CONFIG_PATH_x86_64_unknown_linux_gnu
cargo:rerun-if-env-changed=HOST_PKG_CONFIG_PATH
cargo:rerun-if-env-changed=PKG_CONFIG_PATH
cargo:rerun-if-env-changed=PKG_CONFIG_LIBDIR_x86_64-unknown-linux-gnu
cargo:rerun-if-env-changed=PKG_CONFIG_LIBDIR_x86_64_unknown_linux_gnu
cargo:rerun-if-env-changed=HOST_PKG_CONFIG_LIBDIR
cargo:rerun-if-env-changed=PKG_CONFIG_LIBDIR
cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR_x86_64-unknown-linux-gnu
cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR_x86_64_unknown_linux_gnu
cargo:rerun-if-env-changed=HOST_PKG_CONFIG_SYSROOT_DIR
cargo:rerun-if-env-changed=PKG_CONFIG_SYSROOT_DIR
run pkg_config fail: "`\"pkg-config\" \"--libs\" \"--cflags\" \"openssl\"` did not exit successfully: exit code: 1\n--- stderr\nPackage openssl was not found in the pkg-config search path.\nPerhaps you should add the directory containing `openssl.pc\'\nto the PKG_CONFIG_PATH environment variable\nNo package \'openssl\' found\n"

--- stderr
thread 'main' panicked at '

Could not find directory of OpenSSL installation, and this `-sys` crate cannot
proceed without this knowledge. If OpenSSL is installed and this crate had
trouble finding it, you can set the `OPENSSL_DIR` environment variable for the
compilation process.

Make sure you also have the development packages of openssl installed.
For example, `libssl-dev` on Ubuntu or `openssl-devel` on Fedora.

If you're in a situation where you think the directory *should* be found
automatically, please open a bug at https://github.com/sfackler/rust-openssl
and include information about your system as well as this message.

$HOST = x86_64-unknown-linux-gnu
$TARGET = x86_64-unknown-linux-gnu
openssl-sys = 0.9.61

', /home/xxx/.cargo/registry/src/github.com-1ecc6299db9ec823/openssl-sys-0.9.61/build/find_normal.rs:174:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
warning: build failed, waiting for other jobs to finish...
error: build failed
```

Start by reproducing `cargo build --release` on Ubuntu 20.04 at commit b33c498e99883536519bc01f19d2c6b081eebae1 and read the `openssl-sys` build output. Check how the project declares or documents its OpenSSL build requirements; done means the required setup is clear and the release build succeeds, or the failure is otherwise addressed.

Written by the indexing model from the issue text.