[ELF] Move addWrappedSymbols before postParseObjectFile

addWrappedSymbols may trigger archive extraction: split stack implementation
uses --wrap=pthread_create, which extracts libgcc.a(generic-morestack-thread.o).

This fixes the regression caused by 09602d3b by
making the invariant satisfied: no more non-compileBitcodeFiles object file is
produced at postParseObjectFile.