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It appears you don’t have libffi-dev installed:
sudo apt-get install libffi-dev
Should install the package with the missing header.
If this is a fresh server then you could also opt to install some of the more common dev packages at once:
sudo apt-get install libffi-dev libssl-dev libxml2-dev libxslt1-dev libncurses5-sdev
Source:stackexchange.com