Since a while ago (most likely the CMake changes a few days back, but not sure when this became a problem), the libftdi-config util reports invalid path:

$ /usr/local/bin/libftdi-config --cflags
-I/usr/local/include/libftdi
$ ls -al /usr/local/include/libftdi
ls: /usr/local/include/libftdi: No such file or directory
$ ls -al /usr/local/include/ftdi.h
-rw-r--r--  1 root  wheel  16428 Mar 15  2012 /usr/local/include/ftdi.h
$

CMakeLists.txt from libftdi-0.20 seems to have:

set(includedir  ${CMAKE_INSTALL_PREFIX}/include/${PROJECT_NAME})

However, it does not seem to actually install it in /usr/local/include/libftdi..
However, the attached patch fixes the problem (wronlgy reported include-dir) and I'm now able to compile my program again.

Env: FreeBSD 10.0-RELEASE on amd64.