title: What exactly is crt1.3.1.o
body: <p>I'm using xcode 4.5 My Base SDK is 6.0 and my deployment target is 5.1. When I try to build for release or profiling I get this little gem of an error.</p>
  
  <pre><code>ld: file is universal (4 slices) but does not contain a(n) armv7s slice: /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS5.1.sdk/usr/lib/crt1.3.1.o for architecture armv7s
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  </code></pre>
  
  <p>Now....</p>
  
  <p>I have seen this message posted on stackoverflow but Im still none the wiser.</p>
  
  <p>What exactly is this crt1.2.1.o thats causing all the fuss?
  Can I modify it somehow to kill my error?
  And finally it has been suggested that I simply set build for active architectures only. What are the implications of doing this?</p>
  
  <p>Thanks</p>