[CMake] building an autoconf project with externalproject

[Josh Stratton]

I'm trying to get cmake to compile an autoconf external library that comes
with my git repo.  I've found an example on stackoverflow that supposedly
works, but I get an error message saying no CMakeLists.txt exists in that
directory.

http://stackoverflow.com/questions/16604815/cmake-reuse-externalproject-depends-does-not-work

I figured because BUILD_DIR is set to "make", I wouldn't need a
CMakeLists.txt file in that directory.  Anyway, I tried including an empty
one and get a "no rule to make target install", which is closer, but still
not correct as I'm not calling "make install", right?

Here's my root CMakeLists.txt.  Is there another argument or something to
get this to work?  Why does including "make" give an "install" message?  If
I'm doing the whole autoconf workflow, do I need the full set of commands
"configure; make; make install" or is cmake doing some fancy logic?

cmake_minimum_required(VERSION 2.8)

project(ppml)

include(ExternalProject)

ExternalProject_Add(
  fftw
  DOWNLOAD_COMMAND ""
  SOURCE_DIR /home/stratton/Public/ppml/external/fftw-3.3.3
  BUILD_COMMAND make
  BUILD_IN_SOURCE 1
)
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