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).
* added dynare_simul_ DLL
* factorized in a library object the Dynare++ code shared between gensylv, k_order_perturbation and dynare_simul_
git-svn-id: https://www.dynare.org/svn/dynare/trunk@3114 ac1d8469-bf42-47a9-8791-bf33cf982152