I looked in the usual places (/usr/lib/,/Developer/usr/lib/,/usr/local/lib), and it isn't there.
If it isn't installed, does anyone know where I can find instructions to install it?
Thanks!
I'm not sure if I should close this, but I found the answer I was looking for:
In OS X, with XCode 4 installed, libclang.dylib is at /Developer/usr/clang-ide/lib/libclang.dylib
On macOS Catalina (newest, as of posting) you can find it in the Xcode application, here:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/libclang.dylib
As well as outside of it if you just use Command Line Tools and you don't have Xcode.app installed, here:
/Library/Developer/CommandLineTools/usr/lib/libclang.dylib
As pointed out by @Daco Harkes the Xcode library does not include the Objective C headers, so you might want to use the Command Line Tools version anyway.
Additionally, this uses Apple's build of Clang which can be... quirky and doesn't implement all the newest features. So you might want to download the LLVM version, which you can download from their website or get from Homebrew's LLVM package (brew install llvm).
When installed through Homebrew the library can be found at:
/usr/local/opt/llvm/lib/libclang.dylib