This means we now require GCC 8.

Boost filesystem library is no longer needed.

Ref preprocessor#16

The MEX files are built out-of-tree (because we want to do them in parallel).
This would create a potential race condition if several builds want to create
the symlinks under mex/matlab/ or mex/octave/.

The solution is to disable those symlinks for out-of-tree builds.

The scripts are based the former “dynare-build” project. They have been
overhauled and simplified.

Building a Windows package (both installer and zip archive) is as easy as
running “make -C windows” (provided the right Debian packages are installed,
use the “windows/install-packages.sh” script for that purpose).

The layout of MEX files for Octave in the package has been
changed (mex/octave/win32/ and mex/octave/win64/ instead of mex/octave32/ and
mex/octave/), for consistency with MATLAB MEX.

As a consequence, remove the --enable-openmp option of the configure script.

It constructs the stacked residuals and jacobian of the perfect foresight
problem.

It is an almost perfect replacement for the perfect_foresight_problem.m
routine, while being much more efficient.

Note however that the DLL never return complex numbers (it instead puts NaNs at
the place where there would have been complex). This may create problems for
some MOD files; the algorithms will need to be adapted to use a more
line-search method.

Various modernizations and simplifications.

Also remove a workaround for a LAPACK bug in DGGES (the VSL argument was
apparently referenced even though JOBVSL="N"). Hopefully the bug has been fixed
everywhere now.

Adapt the code accordingly.

We now use a symbolic link farm to make source file accessible from build
directories.

Closes #466

As a consequence, the singleton implementation has to be made thread-safe.

Also implement the singleton pattern using a namespace, rather than a static
instance.

There were two implementations of integer exponentiation. Merge them into a new
file under utils/cc/.

By the way, optimize it using exponentiation by squaring.

On Windows, this means that a POSIX threads implementation is no longer needed,
since C++11 threads are implemented using native Windows threads.

On GNU/Linux and macOS, POSIX threads are still used under the hood.

A new m4 macro (AX_CXX11_THREAD) is used to add the proper compilation
flags (instead of AX_PTHREAD).

By the way apply Dynare C++ coding style and extensions (.cc/.hh).

By the way apply Dynare C++ coding style and extensions (.cc/.hh).

By the way apply Dynare C++ coding style and extensions (.cc/.hh).

Otherwise the DLL is dynamically linked against libwinpthread. This regression
was introduced by commit 671fe4bc.

- Use the -static flag when linking Dynare++, so that shipping libquadmath and
  libgcc DLL in the installer is no longer needed.

- Use AM_CXXFLAGS and AM_LDFLAGS variables for changing flags, since CXXFLAGS
  and LDFLAGS are user variables. Also, this avoids passing these flags down to
  configure scripts in subdirectories.

- Check for the SZIP library in the configure test for the MatIO, this is
  needed under MSYS2.

- Statically link MatIO and GSL in MEX files for MATLAB, this is needed under
  MSYS2.

Needed because bytecode DLL uses some preprocessor code which is C++14.

It's actually not needed. The QZ complex decomposition can be obtained in
Octave on real matrices by casting them to the complex type.