Revert r168519, "Merge used flags so that we don't have to iterate on isUsed. With this change"

It brought bunch of (possibly false) warnings.

llvm/unittests/VMCore/PassManagerTest.cpp:60:22: warning: variable 'ID' is not needed and will not be emitted [-Wunneeded-internal-declaration]
    char ModuleNDNM::ID=0;
                     ^
llvm/unittests/VMCore/PassManagerTest.cpp:86:22: warning: variable 'ID' is not needed and will not be emitted [-Wunneeded-internal-declaration]
    char ModuleNDM2::ID=0;
                     ^
llvm/unittests/VMCore/PassManagerTest.cpp:106:21: warning: variable 'ID' is not needed and will not be emitted [-Wunneeded-internal-declaration]
    char ModuleDNM::ID=0;
                    ^
llvm/unittests/VMCore/PassManagerTest.cpp:217:16: warning: variable 'initcount' is not needed and will not be emitted [-Wunneeded-internal-declaration]
    int LPass::initcount=0;
               ^
llvm/unittests/VMCore/PassManagerTest.cpp:218:16: warning: variable 'fincount' is not needed and will not be emitted [-Wunneeded-internal-declaration]
    int LPass::fincount=0;
               ^
llvm/unittests/VMCore/PassManagerTest.cpp:259:16: warning: variable 'inited' is not needed and will not be emitted [-Wunneeded-internal-declaration]
    int BPass::inited=0;
               ^
llvm/unittests/VMCore/PassManagerTest.cpp:260:16: warning: variable 'fin' is not needed and will not be emitted [-Wunneeded-internal-declaration]
    int BPass::fin=0;
               ^
llvm/unittests/VMCore/PassManagerTest.cpp:283:24: warning: variable 'ID' is not needed and will not be emitted [-Wunneeded-internal-declaration]
    char OnTheFlyTest::ID=0;
                       ^
8 warnings generated.

llvm-svn: 168549