Fix enumerating loaded process modules on Apple platforms (#5487)

- This logic always assumed that the lowest address of a mapped file was
its "base address", but in the presence of dotnet/runtime#114462 that is
no longer correct. We may map stubs at lower addresses.
- Fix by checking the start of the mapped region for the magic value for
the start of a MachO binary

Author: davidwrighton

src/shared/pal/src/thread/process.cpp

@@ -2371,7 +2371,10 @@ CreateProcessModules(
             }
         }
 
-        if (!dup)
+        // Does the offset in the module correspond to a valid MachO header?
+        bool mightBeMachOHeader = rwpi.prp_prinfo.pri_offset == 0;
+
+        if (!dup && mightBeMachOHeader)
         {
             int cbModuleName = strlen(moduleName) + 1;
             ProcessModules *entry = (ProcessModules *)malloc(sizeof(ProcessModules) + cbModuleName);