title: LLVM & Clang can't compile for a supported arch
body: <p>Under Ubuntu 64 bit I got</p>
  
  <pre><code>llc --version
  LLVM (http://llvm.org/):
    LLVM version 3.1
    Optimized build with assertions.
    Built Oct 15 2012 (18:15:59).
    Default target: x86_64-pc-linux-gnu
    Host CPU: btver1
  
    Registered Targets:
      arm      - ARM
      mips     - Mips
      mips64   - Mips64 [experimental]
      mips64el - Mips64el [experimental]
      mipsel   - Mipsel
      thumb    - Thumb
      x86      - 32-bit X86: Pentium-Pro and above
      x86-64   - 64-bit X86: EM64T and AMD64
  </code></pre>
  
  <p>I can't do this</p>
  
  <pre><code>clang -march=arm -x c++ /tmp/cpp.cpp 
  error: unknown target CPU 'arm'
  </code></pre>
  
  <p>I'm missing something here ? Why I can't compile for ARM ?</p>