title: xcrun -sdk iphonesimulator clang unable to cross compile after xcode6-beta7
body: <p>I use "xcrun -sdk iphonesimulator clang" for CC when configuring ffmpeg.</p>
  
  <p>xcrun -sdk iphonesimulator clang is unable to create an executable file.
  If xcrun -sdk iphonesimulator clang is a cross-compiler, use the --enable-cross-compile option.
  Only do this if you know what cross compiling means.
  C compiler test failed.</p>
  
  <p>xcode5 is ok.</p>
  
  <p>=========== Update ========
  I added a test, it seems clang not link _start for simulator.</p>
  
  <pre><code>AGSPC98:pwd fluke$ cat&gt; ~/tmp/ios.c
  int main(void){ return 0; }
  AGSPC98:pwd fluke$ /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -fasm -fno-short-enums -fno-strict-aliasing -arch i386 -miphoneos-version-min=5.0 -g -fno-inline-functions -O0 -falign-functions=4 -DDEBUG=1 -DVPLAYER_IOS=1 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator8.0.sdk -c -o ~/tmp/ios.o ~/tmp/ios.c
  AGSPC98:pwd fluke$ 
  AGSPC98:pwd fluke$ /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator8.0.sdk -arch i386 -miphoneos-version-min=5.0 -o ~/tmp/ios ~/tmp/ios.o
  Undefined symbols for architecture i386:
    "start", referenced from:
       implicit entry/start for main executable
  ld: symbol(s) not found for architecture i386
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  AGSPC98:pwd fluke$ nm ~/tmp/ios.o 
  00000000 T _main
  </code></pre>