Use brew version of libtoolize.

Brewfile

@@ -1,5 +1,6 @@
 brew "libsodium"
 brew "json-c"
 
+brew "libtool"
 brew "automake"
 brew "autoconf"

lib/bin/build_lib

@@ -50,7 +50,7 @@ _initialize() {
 #
 # Check if all tools needed for the default implementations are available.
 #
-# By default, this will check for `automake` (for aclocal) and `autoconf` (for autoreconf).
+# By default, this will check for `libtool` (for libtoolize), `automake` (for aclocal) and `autoconf` (for autoreconf).
 initialize_needs() { _initialize_needs "$@"; }
 _initialize_needs() {
     if [[ $platform = windows ]]; then
@@ -58,7 +58,7 @@ _initialize_needs() {
         export VSINSTALLDIR="${VSINSTALLDIR:-$(cd "$(cygpath -F 0x002a)/Microsoft Visual Studio"/*/*/Common7/.. && pwd)}"
         [[ -e "$VSINSTALLDIR/Common7/Tools/VsMSBuildCmd.bat" ]] || { echo >&2 "Missing: msbuild.  Please install 'Build Tools for Visual Studio'."; return 1; }
     else
-        needs automake autoconf
+        needs libtool automake autoconf
     fi
 }