Fix linker-defined symbols possibly not being defined when -wrap is used

Fixes https://bugs.llvm.org/show_bug.cgi?id=40134

addWrappedSymbols() must be called before addReservedSymbols() because the
latter only defines reserved symbols when they are undefined in the symbol
table. If addWrappedSymbols() is called after, then addUndefined() is called
which may lazily pull in more object files that could reference reserved
symbols.

Differential Revision: https://reviews.llvm.org/D56110

llvm-svn: 350251