m4 is also not currently included by AOSP

static/build.html

@@ -236,9 +236,11 @@
             process is being phased out by using the same LLVM toolchain as building and linking
             for the target.</p>
 
-            <p>Android Open Source Project build dependencies:</p>
+            <p>Additional Android Open Source Project build dependencies not provided by the
+            source tree:</p>
 
             <ul>
+                <li>m4 (will be included as a prebuilt in the next major release)</li>
                 <li>python2 (being replaced with python3 for the next major release)</li>
             </ul>