Script to install cURL CA certificates on OS X without macports

mac-curl-ca-bundle.sh

#!/bin/bash
mkdir /tmp/curl-ca-bundle
cd /tmp/curl-ca-bundle
wget http://curl.haxx.se/download/curl-7.22.0.tar.bz2
tar xzf curl-7.22.0.tar.bz2
cd curl-7.22.0/lib/
./mk-ca-bundle.pl
if [ ! -d /usr/share/curl/ ]; then
	sudo mkdir -p /usr/share/curl/
else
	sudo mv /usr/share/curl/ca-bundle.crt /usr/share/curl/ca-bundle.crt.original
fi
sudo mv ca-bundle.crt /usr/share/curl/ca-bundle.crt
echo
echo "Done!"

Setting /set weechat.network.gnutls_ca_file "/usr/local/etc/openssl/cert.pem" as in WeeChat FAQ works for me. Homebrew OpenSSL Caveats says:

==> Caveats
A CA file has been bootstrapped using certificates from the SystemRoots
keychain. To add additional certificates (e.g. the certificates added in
the System keychain), place .pem files in
  /usr/local/etc/openssl/certs

and run
  /usr/local/opt/openssl/bin/c_rehash

This formula is keg-only, which means it was not symlinked into /usr/local,
because Apple has deprecated use of OpenSSL in favor of its own TLS and crypto libraries.

If you need to have this software first in your PATH run:
  echo 'export PATH="/usr/local/opt/openssl/bin:$PATH"' >> ~/.zshrc

For compilers to find this software you may need to set:
    LDFLAGS:  -L/usr/local/opt/openssl/lib
    CPPFLAGS: -I/usr/local/opt/openssl/include
For pkg-config to find this software you may need to set:
    PKG_CONFIG_PATH: /usr/local/opt/openssl/lib/pkgconfig

Confirming that solution provided by @oblitum works. Many thanks!