[gdb/symtab] Note errors in process_skeletonless_type_units

With a hello world a.out, and using the compiler flags from target board
dwarf5-fission-debug-types:
...
$ gcc -gdwarf-5 -fdebug-types-section -gsplit-dwarf ~/data/hello.c
...
I run into:
...
$ gdb -q -batch a.out
terminate called after throwing an instance of 'gdb_exception_error'
...

What happens is that an error is thrown due to invalid dwarf, but the error is
not caught, causing gdb to terminate.

In a way, this is a duplicate of PR32861, in the sense that we no longer run
into this after:
- applying the proposed patch (work around compiler bug), or
- using gcc 9 or newer (compiler bug fixed).

But in this case, the failure mode is worse than in PR32861.

Fix this by catching the error in
cooked_index_worker_debug_info::process_skeletonless_type_units.

With the patch, we get instead:
...
$ gdb -q -batch a.out
Offset from DW_FORM_GNU_str_index or DW_FORM_strx pointing outside of \
  .debug_str.dwo section in CU at offset 0x0 [in module a.out]
...

While we're at it, absorb the common use of
cooked_index_worker_result::note_error:
...
  try
    {
      ...
    }
  catch (gdb_exception &exc)
    {
      (...).note_error (std::move (exc));
    }
...
into the method and rename it to catch_error, resulting in more compact code
for the fix:
...
  (...).catch_error ([&] ()
    {
      ...
    });
...

While we're at it, also use it in
cooked_index_worker_debug_info::process_units which looks like it needs the
same fix.

Tested on x86_64-linux.

PR symtab/32979
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32979

gdb/dwarf2/read.c

@@ -3425,7 +3425,10 @@ cooked_index_worker_debug_info::process_type_units
 			  abbrev_table.get (), nullptr, false,
 			  language_minimal);
       if (!reader.is_dummy ())
-	process_type_unit (&reader, storage);
+	storage->catch_error ([&] ()
+	  {
+	    process_type_unit (&reader, storage);
+	  });
     }
 }
 
@@ -3467,7 +3470,10 @@ cooked_index_worker_debug_info::process_skeletonless_type_units
   if (per_objfile->per_bfd->dwp_file == nullptr)
     for (const dwo_file_up &file : per_objfile->per_bfd->dwo_files)
       for (const dwo_unit_up &unit : file->tus)
-	process_skeletonless_type_unit (unit.get (), per_objfile, storage);
+	storage->catch_error ([&] ()
+	  {
+	    process_skeletonless_type_unit (unit.get (), per_objfile, storage);
+	  });
 }
 
 void
@@ -3486,14 +3492,10 @@ cooked_index_worker_debug_info::process_units (size_t task_number,
     {
       dwarf2_per_cu *per_cu = inner->get ();
 
-      try
+      thread_storage.catch_error ([&] ()
 	{
 	  process_unit (per_cu, m_per_objfile, &thread_storage);
-	}
-      catch (gdb_exception &except)
-	{
-	  thread_storage.note_error (std::move (except));
-	}
+	});
     }
 
   thread_storage.done_reading (complaint_handler.release ());