Really fix: <rdar://problem/8361834> MacroInfo::AddTokenToBody() leaks memory

The problem was not the management of MacroInfo objects, but that when we recycle them
via the MICache the memory of the underlying SmallVector (within MacroInfo) was not getting
released.  This is because objects stashed into MICache simply are reused with a placement
new, and never have their destructor called.

llvm-svn: 116862