Tried to make it a little intelligent.

Shoot in the dark.

Got:
Marlin_main.cpp:2567: warning: unused variable 'codepos'

Needs revision.
Don't now how this should look like.

Got:
Marlin_main.cpp:1689: warning: 'codenum' may be used uninitialized in this function

And indeed codenum is undefined when no parameter is given.

got:
Marlin_main.cpp:387: warning: 'delta' defined but not used

Compiles cleaner when definition is removed.

got:
ultralcd.cpp:408: warning: 'void lcd_autostart_sd()' defined but not used

Got:
ultralcd.cpp:64: warning: 'void lcd_control_retract_menu()' declared 'static' but never defined

While bunting an other bug I stumbled across:
ultralcd.cpp:1250: warning: comparison between signed and unsigned
integer expressions
Changed to the type of lcd_next_update_millis.

Users hat to press kill-button for unexpexted lon times.
See #1593

with sources in /fonts

The Check Endstop logic must be:

if (current_block->steps_x != current_block->steps_y || (TEST(out_bits,
X_AXIS) == TEST(out_bits, Y_AXIS)))
if (TEST(out_bits, X_HEAD))

not

if (TEST(out_bits, X_HEAD) && (current_block->steps_x !=
current_block->steps_y || (TEST(out_bits, X_AXIS) == TEST(out_bits,
Y_AXIS))))

Same applies for Y axis.

Thank you @Nprod.

and some more comments

in dogm_lcd_implementation.h
by using standard font and
shifting down temperature displays by one pixel
Saves 2300 bytes.

- Compare pr_char to space
- Fewer calls to lcd_strlen

- Get rid of _selected functions, passing selected state instead

- Addressing issue #1608

Warning: suggest parentheses around comparison in operand of &

pretty much helped.

- Add support for 4th extruder
- Fix parentheses matching
- Apply coding standards
- Address issue mentioned at #1575

- Add BIT and TEST macros
- Add _APPLY_ macros to stepper.cpp to help with consolidation
- Consolidate code in stepper.cpp using macros
- Apply standards in stepper.cpp
- Use >= 0 instead of > -1 as a better semantic
- Replace DUAL_Y_CARRIAGE with Y_DUAL_STEPPER_DRIVERS

Cleaned typo in language_test.h Cyrillic part.

- Make separate get_pid_output(e) and get_pid_output_bed() function
- Reduce size of manage_heater function
- Hopefully work around linker errors