Use unique_ptr to own MCFunctions within MCModule.

MCModule's ctor had to be moved out of line so the definition of
MCFunction was available. (ctor requires the dtor of members (in case
the ctor throws) which required access to the dtor of MCFunction)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206244 91177308-0d34-0410-b5e6-96231b3b80d8