OSX ships with curl and installing parallel versions via Homebew can cause all kinds of trouble.
Homebrew comes with the .pc meta file for libcurl in both Mountain Lion and Leopard and it is advisable to just reuse them where possible.
A really simple approach would be to include the Homebrew’s meta file as part of the search path for pkg-config. So in addition to the default searches in /usr/lib/pkgconfig, /usr/share/pkgconfig, /usr/local/lib/pkgconfig and /usr/local/share/pkgconfig, pkg-config will now include your new paths.
export PKG_CONFIG_PATH=/usr/local/Library/ENV/pkgconfig/mountain_lion/
something else 