Exit handler is not invoked for FreeCAD.exe

**Describe the bug**

The exit event handler is not invoked when FreeCAD.exe (the target GUI program) terminates. It terminates normally - as a result of closing the window with mouse-click.

(Sorry, I didn't know what keyword to use in the title, because this case doesn't match any keyword exactly.)

**To Reproduce**

We can use the following simple client to show the problem (compiled in the standard cmake way for DR):

```
#include
#include

void event_exit() {
FILE *f = fopen("tmp", "a");
fprintf(f, "EXIT\n");
fclose(f);
}

DR_EXPORT void dr_client_main(client_id_t id, int argc, const char *argv[]) {
FILE *f = fopen("tmp", "a");
fprintf(f, "MAIN\n");
fclose(f);
dr_register_exit_event(event_exit);
}
```

Run this command, wait until the end of FreeCAD initialization, then close the window (drrun and freecad processes will finish):
```
drrun.exe -c client.dll -- FreeCAD.exe
```

After that, the tmp file contains "MAIN", but does not contain "EXIT".

**Expected behavior**

The exit handler must be called.

**Versions**

DynamoRIO - version 8.0.0-1 (binary release downloaded from the official website)

OS Windows 10 - version 20H2 (build 19042.804)
This is a VirtualBox machine by Microsoft:
https://developer.microsoft.com/en-us/windows/downloads/virtual-machines/

FreeCAD 0.18.4 (x86-64) (installed by the installer from the official website)
https://www.freecadweb.org
https://github.com/FreeCAD/FreeCAD/releases/download/0.18.4/FreeCAD-0.18.4.980bf90-WIN-x64-installer.exe

**Additional context**

This problem is specific for FreeCAD; the exit handler is invoked normally for other targets (simple console programs or GUI programs, for example, Notepad).

I can see the problem even without any client - for example, using this command:
```
drrun.exe -debug -- FreeCAD.exe 1> output 2>&1
```

The output file content:
```

FreeCAD 0.18, Libs: 0.18R4 (GitTag)
В© Juergen Riegel, Werner Mayer, Yorik van Havre 2001-2019
##### #### ### ####
# # # # # #
# ## #### #### # # # # #
#### # # # # # # # ##### # #
# # #### #### # # # # #
# # # # # # # # # ## ## ##
# # #### #### ### # # #### ## ## ##
```

It doesn't contain phrase `` as for other applications.