Warnings on High Sierra related to libssl / libcrypto

[mnshkv]

After running crystal play I have some warnings:

Desktop/mobile/network  master ✔                                          1d  ⍉
▶ crystal play
Listening on http://localhost:8080
Package libssl was not found in the pkg-config search path.
Perhaps you should add the directory containing `libssl.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libssl' found
Package libcrypto was not found in the pkg-config search path.
Perhaps you should add the directory containing `libcrypto.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libcrypto' found

Anything else is working fine (not tested ssl-related functionality). I notice the bug after updating to High Sierra.

Crystal version:

▶ crystal -v
Crystal 0.23.1 (2017-09-18) LLVM 4.0.1

Installed with homebrew. I also have installed openssl with brew install openssl

[akzhan]

Duplicate of #4745.