Ensure pthread.h still exists in the include directories by adding it to the extrasdk-...-install phase. 
Ensure pthread.h still exists in the include directories by adding it to the extrasdk-...-install phase. 

TEST=
rm -rf hg/toolchain directories
tools/llvm/utman.sh download-trusted
tools/llvm/utman.sh all
tools/llvm/utman.sh test-all // passes (even for tests that #include<pthread.h>)
tools/llvm/utman.sh all // previously would nuke pthread.h
tools/llvm/utman.sh test-all // still passes


Review URL: http://codereview.chromium.org/2806062

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@2777 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

nacl-webkit/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client