macOS package: fixes related to flex and bison in Homebrew

(manually cherry picked from commit 80460af6)

README.md

@@ -348,5 +348,5 @@ folder where you want Dynare installed.
 - `make -j`
 - **(Optional)** To then build mex files for Octave, run
      - `cd mex/build/octave`
-     - `CC=gcc-9 CXX=g++-9 ./configure --with-matio=/usr/local --with-gsl=/usr/local --with-slicot=/usr/local LDFLAGS=-L/usr/local/lib`
+     - `CC=gcc-9 CXX=g++-9 ./configure --with-matio=/usr/local --with-gsl=/usr/local --with-slicot=/usr/local LDFLAGS=-L/usr/local/lib LEX=/usr/local/opt/flex/bin/flex YACC=/usr/local/opt/bison/bin/bison`
      - `make -j`

macOS/build.sh

@@ -69,6 +69,8 @@ CC=$CC CXX=$CXX ./configure \
   PACKAGE_STRING="dynare $VERSION" \
   CXXFLAGS=-I/usr/local/include \
   LDFLAGS=-static-libgcc \
+  LEX=/usr/local/opt/flex/bin/flex \
+  YACC=/usr/local/opt/bison/bin/bison \
   --with-gsl="$LIB64"/gsl \
   --with-matio="$LIB64"/matio \
   --with-slicot="$LIB64"/Slicot/with-underscore \

preprocessor @ bfc002a0

-Subproject commit 5365cc3b86e0cb447d7c10d1b1ba83d1914dec74
+Subproject commit bfc002a054ad44449671ef2bc54d5fe9f2202138