[gdb] Add const to catch gdb_exception

I did a review of lines containing "catch (gdb_exception" and found a few
where we can add const.

Tested on x86_64-linux.

Approved-By: Tom Tromey <tom@tromey.com>

gdb/exec.c

@@ -294,7 +294,7 @@ validate_exec_file (int from_tty)
 	      symbol_file_add_main (exec_file_target.c_str (), add_flags);
 	      exec_file_attach (exec_file_target.c_str (), from_tty);
 	    }
-	  catch (gdb_exception_error &err)
+	  catch (const gdb_exception_error &err)
 	    {
 	      warning (_("loading %ps %s"),
 		       styled_string (file_name_style.style (),

gdb/python/py-breakpoint.c

@@ -611,7 +611,7 @@ bppy_set_condition (PyObject *self, PyObject *newvalue, void *closure)
     {
       set_breakpoint_condition (self_bp->bp, exp, 0, false);
     }
-  catch (gdb_exception &ex)
+  catch (const gdb_exception &ex)
     {
       GDB_PY_SET_HANDLE_EXCEPTION (ex);
     }
@@ -677,7 +677,7 @@ bppy_set_commands (PyObject *self, PyObject *newvalue, void *closure)
       counted_command_line lines = read_command_lines_1 (reader, 1, nullptr);
       breakpoint_set_commands (self_bp->bp, std::move (lines));
     }
-  catch (gdb_exception &ex)
+  catch (const gdb_exception &ex)
     {
       GDB_PY_SET_HANDLE_EXCEPTION (ex);
     }

gdb/python/py-inferior.c

@@ -631,7 +631,7 @@ infpy_write_memory (PyObject *self, PyObject *args, PyObject *kw)
 
       write_memory_with_notification (addr, buffer, length);
     }
-  catch (gdb_exception &ex)
+  catch (const gdb_exception &ex)
     {
       GDB_PY_HANDLE_EXCEPTION (ex);
     }
@@ -705,7 +705,7 @@ infpy_search_memory (PyObject *self, PyObject *args, PyObject *kw)
 				    buffer, pattern_size,
 				    &found_addr);
     }
-  catch (gdb_exception &ex)
+  catch (const gdb_exception &ex)
     {
       GDB_PY_HANDLE_EXCEPTION (ex);
     }

gdb/python/py-value.c

@@ -1178,7 +1178,7 @@ valpy_getitem (PyObject *self, PyObject *key)
       if (res_val)
 	result = value_to_value_object (res_val);
     }
-  catch (gdb_exception &ex)
+  catch (const gdb_exception &ex)
     {
       GDB_PY_HANDLE_EXCEPTION (ex);
     }
@@ -1704,7 +1704,7 @@ valpy_nonzero (PyObject *self)
 	/* All other values are True.  */
 	nonzero = 1;
     }
-  catch (gdb_exception &ex)
+  catch (const gdb_exception &ex)
     {
       /* This is not documented in the Python documentation, but if
 	 this function fails, return -1 as slot_nb_nonzero does (the

gdb/unittests/scoped_mmap-selftests.c

@@ -114,7 +114,7 @@ test_invalid_filename ()
 
   try {
       ::scoped_mmap m = ::mmap_file ("/this/file/should/not/exist");
-  } catch (gdb_exception &e) {
+  } catch (const gdb_exception &e) {
       threw = true;
   }