Fix duplicate shared module list entries

[ADodds]

Summary

The POSIX DYLD has a fault causing it to duplicate all of the shared module entries twice. This happens because DYLDRendezvous::TakeSnapshot is called twice upon attach, and it appends to the list each time, rather then replacing its contents. This is fixed by clearing the list before taking a new snapshot.

[clayborg]

Looks good.

lldb/trunk/source/Plugins/DynamicLoader/POSIX-DYLD/DYLDRendezvous.cpp

 bool
 DYLDRendezvous::TakeSnapshot(SOEntryList &entry_list)
 {
     SOEntry entry;
 
     if (m_current.map_addr == 0)
         return false;
 
+    // Clear previous entries since we are about to obtain an up to date list.
+    entry_list.clear();
+
     for (addr_t cursor = m_current.map_addr; cursor != 0; cursor = entry.next)
     {
         if (!ReadSOEntryFromMemory(cursor, entry))
             return false;
 
         // Only add shared libraries and not the executable.
         if (SOEntryIsMainExecutable(entry))
             continue;