[J-core] nextpnr build failed with weird cmake error?

[Rob Landley]

Jeff, I'm trying to add icestorm and nextpnr to the toolchain build, following
your model, and I got:

-- Looking for sys/types.h
CMake Error at /usr/share/cmake-3.7/Modules/CheckIncludeFile.cmake:56 (try_compile):
  Unknown extension ".c" for file

    /home/landley/yogh2/sub2/nextpnr/CMakeFiles/CMakeTmp/CheckIncludeFile.c

  try_compile() works only for enabled languages.  Currently these are:

    CXX

Does this sound familiar? (This is _after_ I installed
libboost{,thread,system,iostreams,rogram-options,filesystem}-dev libeigen3-dev
for this monster...)

It's using more or less your build invocation:

cd nextpnr &&
cmake . -DARCH="ice40" -DCMAKE_INSTALL_PREFIX="$PREFIX" \
  -DICESTORM_INSTALL_PREFIX="$PREFIX" -DBUILD_GUI=OFF -DBUILD_PYTHON=OFF \
  -DSTATIC_BUILD=ON &&
make -j $(nproc) &&
cd .. || exit 1

Rob