Fix libLTO:

 * Call InitializeAllTargets on every path where we might query the
   TargetRegistry. This fixes PR4604.
 * flush the formatted_raw_ostream& or else not all of the assembly will make
   it to the .s file. (It doesn't do this in its destructor?!)
 * Due to a reversed conditional, libLTO was reporting many symbols as both
   defined and undefined, including two definitions of the same symbol name
   in its symbol list.

llvm-svn: 77170