Quick cmake configuring/building/testing instructions for Unix (Linux/OSX/*BSD)

Parameters:

WITH_NTL (yes/no) - builds Flint with NTL support

BUILD_TESTING (yes/no) - build tests

CMAKE_BUILD_TYPE - type of the build

Typically cmake buildig is done in a clean subdirectory:

    mkdir build 
    cd build
    # creates a debug build of Flint without NTL support
    cmake -G"Unix Makefiles" ..

At the end of cmake run, it says where the build is located; in some settings it might be in the
main Flint directory, i.e. you would have to

    cd ..

    make -j4    # builds Flint in lib/

    # creates a release build of Flint with NTL support and tests
    cmake -G"Unix Makefiles" -DWITH_NTL=yes -DBUILD_TESTING=yes -DCMAKE_BUILD_TYPE=Release ..
    make -j4    # builds Flint in lib/
    make test   # runs Flint tests  - this takes a while

It is apparently more efficient to run tests directly using ctest, it will try to run slower
tests first:

    ctest -j4 # on 4 cores

before running make. More details about parallel builds may be found in
https://blog.kitware.com/cmake-building-with-all-your-cores/

