[lldb] Prevent early exit for weak symbol found in IRExecutionUnit::FindInSymbols

`LoadAddressResolver::Resolve` returns zero for weak symbols. However `FindInSymbols`
does multiple searches (each starting with `FindSymbolsWithNameAndType`), and a resolved
address of zero from one step of the search should not conclude the search.

This change continues the searching for a symbol by only performing an early exit when a
concrete address is found.

This was identified by an objc class which is available only in newer OSes. Such classes
are weak linked. Expressions involving this class were failing, because the search first
found the weak linked symbol.

rdar://161406615

Author: kastiglione

lldb/source/Expression/IRExecutionUnit.cpp

@@ -822,23 +822,26 @@ IRExecutionUnit::FindInSymbols(const std::vector<ConstString> &names,
       sc.module_sp->FindSymbolsWithNameAndType(name, lldb::eSymbolTypeAny,
                                                sc_list);
       if (auto load_addr = resolver.Resolve(sc_list))
-        return *load_addr;
+        if (!symbol_was_missing_weak)
+          return *load_addr;
     }
 
     {
       SymbolContextList sc_list;
       m_preferred_modules.FindSymbolsWithNameAndType(name, lldb::eSymbolTypeAny,
                                                      sc_list);
       if (auto load_addr = resolver.Resolve(sc_list))
-        return *load_addr;
+        if (!symbol_was_missing_weak)
+          return *load_addr;
     }
 
     {
       SymbolContextList sc_list;
       non_local_images.FindSymbolsWithNameAndType(name, lldb::eSymbolTypeAny,
                                                   sc_list);
       if (auto load_addr = resolver.Resolve(sc_list))
-        return *load_addr;
+        if (!symbol_was_missing_weak)
+          return *load_addr;
     }
 
     lldb::addr_t best_internal_load_address =