Base.hsc:103:10: fatal error: 'pcre.h' file not found
After googling around for a bit I came across this thread on Stackoverflow which had the same missing header file error, but which had nothing to do with Haskell. So from the sounds of things I just needed to install the PCRE library on my Mac.
I installed PCRE on MacOSX with:
brew install pcre
cabal install --only-dependencies completed successfully. Yay! :)