autogen.sh invoker to build libqalculate on macos+homebrew

autoautogen.sh

#!/usr/bin/env bash

for pkg in gmp mpfr icu4c readline; do
  PREFIX="$(brew --prefix $pkg)"
  CPPFLAGS="$CPPFLAGS -I$PREFIX/include"
  LDFLAGS="$LDFLAGS -L$PREFIX/lib"
  PKG_CONFIG_PATH="$PKG_CONFIG_PATH:$PREFIX/lib/pkgconfig"
done

export CPPFLAGS LDFLAGS PKG_CONFIG_PATH

export CXXFLAGS="-std=c++17"

./autogen.sh