title: GNU assembler not found, install/update gas-preprocessor
body: <p>I want to cross compile FFmpeg using clang. Here is part of my configure.</p>
  
  <pre><code> ./configure --cross-prefix=${TOOLCHAIN}/bin/arm-linux-androideabi-
  </code></pre>
  
  <p>The var <code>TOOLCHAIN</code> is tool chain dir. After configured, the output is.</p>
  
  <pre><code> C compiler                toolchains/bin/arm-linux-androideabi-gcc
   C library                 bionic
   host C compiler           gcc
   host C library            
  </code></pre>
  
  <p>I want to change compiler to <code>clang</code>. So I <code>export CC=${TOOLCHAIN}/bin/clang</code>. However the configuration is keeping <code>gcc</code>. How can I use clang and clang++ compiler?</p>
  
  <p>I tried to configure <code>CC</code> like this.</p>
  
  <pre><code>--cc="${TOOLCHAINS_PREFIX}/bin/clang"
  </code></pre>
  
  <p>But I got an error.</p>
  
  <blockquote>
    <p>GNU assembler not found, install/update gas-preprocessor</p>
  </blockquote>
  
  <p>Thanks in advance.</p>
  
  <h1>EDIT</h1>
  
  <p>I tried <code>--disable-asm</code> then I can pass configuration test. But the generated libs's size increased.</p>