add back macOS script for building boost libraries

boost_libs=<library> install-boost.sh --build

partically revert "drop boost regex lib for windows and macos (rime#735)"

This reverts install-boost.sh from commit 298a9dd.

install-boost.sh

@@ -21,6 +21,18 @@ download_boost_source() {
     [[ -f "${BOOST_ROOT}/bootstrap.sh" ]]
 }
 
+boost_cxxflags='-arch arm64 -arch x86_64'
+
+build_boost_macos() {
+    [[ -n "${boost_libs}" ]] || return
+    cd "${BOOST_ROOT}"
+    ./bootstrap.sh --with-toolset=clang --with-libraries="${boost_libs}"
+    ./b2 -q -a link=static architecture=arm cxxflags="${boost_cxxflags}" stage
+    for lib in stage/lib/*.a; do
+        lipo $lib -info
+    done
+}
+
 if [[ $# -eq 0 || " $* " =~ ' --download ' ]]; then
     if [[ ! -f "${BOOST_ROOT}/bootstrap.sh" ]]; then
         download_boost_source
@@ -31,3 +43,8 @@ if [[ $# -eq 0 || " $* " =~ ' --download ' ]]; then
     ./bootstrap.sh
     ./b2 headers
 fi
+if [[ $# -eq 0 || " $* " =~ ' --build ' ]]; then
+    if [[ "$OSTYPE" =~ 'darwin' ]]; then
+        build_boost_macos
+    fi
+fi