Add note about following two commands are no longer equivalent.
 - "clang -O3 -flto a.c -c", and 
 - "clang -emit-llvm a.c -c" 

Thank Rafael for tips.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189150 91177308-0d34-0410-b5e6-96231b3b80d8