Bug fix, reload modules before getting thread local storage

Summary:
Debugged locally with 2 scenario:
* Load core only, and then auto-load-debuginfo, then can reproduce the error:
    ```
    (lldb) target var HPHP::s_stackSize
    (size_t) HPHP::s_stackSize = <No TLS data currently exists for this thread.>
    ```
* Load core with executable manually, thread local variable is able to be show:
```
(lldb) target var HPHP::s_stackSize
(size_t) HPHP::s_stackSize = 0
```

The root cause is that the [link_map](https://www.internalfb.com/code/osmeta-external-llvm-project/[toolchain%2Fllvm-sand%2Fmain%3A55d44adeadd8500af2335ac99a9b10d1414f47e4]/lldb/source/Plugins/DynamicLoader/ModuleList-DYLD/DynamicLoaderDumpWithModuleList.cpp?lines=284) in the first scenario was 0. Because when the target was created, [DYLDRenzdevous can not be resolved](https://www.internalfb.com/code/osmeta-external-llvm-project/[toolchain%2Fllvm-sand%2Fmain%3A55d44adeadd8500af2335ac99a9b10d1414f47e4]/lldb/source/Plugins/DynamicLoader/ModuleList-DYLD/DynamicLoaderDumpWithModuleList.cpp?lines=120) because of lacking main executable. After auto-load-debuginfo, even we called target module replace, we never have a chance to call DYLDRenzdevous again to resolve and update link map address.

So calling DidAttach() if m_rendezvous is not valid at the very beginning of GetThreadLocalData function is the easiest fix, to have a chance to update the link_map_addr in m_loaded_modules after we have the executable object file replaced by the auto-load-debuginfo command.

Test Plan:
Before this diff:
```
(lldb) target create --core "k9vc79dn9h6pe2y9"
Core file '/home/hyubo/test/k9vc79dn9h6pe2y9' (x86_64) was loaded.
(lldb) auto-load-debuginfo
...
(lldb) target var HPHP::s_stackSize
(size_t) HPHP::s_stackSize = <No TLS data currently exists for this thread.>
```
After this diff:
```
(lldb) target create --core "k9vc79dn9h6pe2y9"
Core file '/home/hyubo/test/k9vc79dn9h6pe2y9' (x86_64) was loaded.
(lldb) auto-load-debuginfo
...
(lldb) target var HPHP::s_stackSize
(size_t) HPHP::s_stackSize = 0
```

Reviewers: jeffreytan, gclayton, #lldb_team

Reviewed By: jeffreytan

Subscribers: michristensen, #lldb_team

Differential Revision: https://phabricator.intern.facebook.com/D56793922

Tasks: T186207554

Tags: accept2ship

Author: George Hu

lldb/source/Commands/CommandObjectTarget.cpp

@@ -42,6 +42,7 @@
 #include "lldb/Symbol/UnwindPlan.h"
 #include "lldb/Symbol/VariableList.h"
 #include "lldb/Target/ABI.h"
+#include "lldb/Target/DynamicLoader.h"
 #include "lldb/Target/Process.h"
 #include "lldb/Target/RegisterContext.h"
 #include "lldb/Target/SectionLoadList.h"
@@ -2943,8 +2944,14 @@ class CommandObjectTargetModulesReplace : public CommandObjectParsed {
 
     if (flush) {
       ProcessSP process = target.GetProcessSP();
-      if (process)
+      if (process) {
         process->Flush();
+        // DYLD rendezvous might not be resolved, try to load all modules again
+        // as we might have main executable replaced.
+        DynamicLoader *dyld = process->GetDynamicLoader();
+        if (dyld)
+          dyld->DidAttach();
+      }
     }
     return;
   }