Remove const_casts by making spec_begin()/spec_end() const


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175159 91177308-0d34-0410-b5e6-96231b3b80d8
Remove an unneeded const_cast


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175160 91177308-0d34-0410-b5e6-96231b3b80d8
Remove a const_cast by propagating constness to called functions


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175161 91177308-0d34-0410-b5e6-96231b3b80d8