macOS package: fixes related to flex and bison in Homebrew

Also mention in the README that sphinx-doc must be linked, since it is
keg-only.

README.md

@@ -414,6 +414,7 @@ xcode-select --install
 - Install required Homebrew packages. Open Terminal.app and type:
 ```sh
 brew install automake bison flex boost gcc gsl libmatio veclibfort octave sphinx-doc wget
+brew link --force sphinx-doc
 ```
 - Compile and install SLICOT, needed for the `kalman_steady_state` MEX file.
 Still from Terminal.app:
@@ -441,7 +442,7 @@ autoreconf -si
 ```
 - Configure Dynare from the source directory:
 ```sh
-./configure --with-matlab=<…> CC=gcc-10 CXX=g++-10 CPPFLAGS=-I/usr/local/include LDFLAGS=-L/usr/local/lib`
+./configure --with-matlab=<…> CC=gcc-10 CXX=g++-10 CPPFLAGS=-I/usr/local/include LDFLAGS=-L/usr/local/lib` LEX=/usr/local/opt/flex/bin/flex YACC=/usr/local/opt/bison/bin/bison'
 ```
 where the path to MATLAB is specified, typically of the form
 `/Applications/MATLAB_R2020b.app`. If you don’t have MATLAB, simply replace

macOS/build.sh

@@ -71,6 +71,8 @@ cd "$ROOTDIR"
   CXX=$CXX \
   CPPFLAGS=-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

@@ -1 +1 @@
-Subproject commit a9daec1c0739f244e2e041f20443af6a6fae555d
+Subproject commit f5760c33ea6e97c9c110be17a64547b0c91ee9b2