Windows package: restore several missing MEX files

Since 533a4ff7, several MEX files were missing
in the Windows package (gensylv, k-order, dynare_simul, MS-SBVAR). The problem
was that the environment variable containing the directory containing MSYS2
libraries (incl. matio and gsl) was not correctly passed to parallelized
subshells.

windows/build.sh

@@ -219,7 +219,7 @@ NTHREADS=$((NTHREADS/${#TASKS[@]}))
 # Build all the mex files (parallel).
 # Some variables and functions need to be available in subshells.
 cd "$ROOT_DIRECTORY"
-export TMP_DIRECTORY ROOT_DIRECTORY LIB32 LIB64 VERSION NTHREADS
+export TMP_DIRECTORY ROOT_DIRECTORY LIB32 LIB32_MSYS2 LIB64 LIB64_MSYS2 VERSION NTHREADS
 export -f "${TASKS[@]}"
 parallel "set -ex;shopt -s globstar;" ::: "${TASKS[@]}"