[Keyboard] Helix use `post_rules.mk` (#14216)

* Helix/pico use post_rules.mk insted of local_features.mk

Tested with the following procedure.
```
git checkout 77a93fec79 (qmk/develop)
make clean
make helix/pico:all:check-md5
make helix/pico/sc:all:check-md5
git checkout helix_use_post_rules.mk
make clean
make helix/pico:all:check-md5
make helix/pico/sc:all:check-md5
```

* Helix/rev2 use post_rules.mk

Tested with the following procedure.
```
git checkout 77a93fec79 (qmk/develop)
make clean
make helix/pico:all:check-md5
make helix/pico/sc:all:check-md5
make helix/rev2:all:check-md5
make helix/rev2/sc:all:check-md5
git checkout helix_use_post_rules.mk
make clean
make helix/pico:all:check-md5
make helix/pico/sc:all:check-md5
make helix/rev2:all:check-md5
make helix/rev2/sc:all:check-md5
```

1 files changed, 147 insertions, 0 deletions

diff --git a/keyboards/helix/pico/post_rules.mk b/keyboards/helix/pico/post_rules.mk
new file mode 100644
index 0000000000..38573d75a5
--- /dev/null
+++ b/keyboards/helix/pico/post_rules.mk
@@ -0,0 +1,147 @@
+#
+#  post_rules.mk contains post-processing rules for the Helix keyboard.
+#
+#   Post-processing rules convert keyboard-specific shortcuts (that represent
+#   combinations of standard options) into QMK standard options.
+#
+
+define HELIX_CUSTOMISE_MSG
+  $(info Helix Spacific Build Options)
+  $(info -  OLED_ENABLE          = $(OLED_ENABLE))
+  $(info -  LED_BACK_ENABLE      = $(LED_BACK_ENABLE))
+  $(info -  LED_UNDERGLOW_ENABLE = $(LED_UNDERGLOW_ENABLE))
+  $(info -  LED_ANIMATIONS       = $(LED_ANIMATIONS))
+  $(info -  IOS_DEVICE_ENABLE    = $(IOS_DEVICE_ENABLE))
+  $(info )
+endef
+
+define HELIX_HELP_MSG
+  $(info Helix keyboard convenient command line option)
+  $(info -    make HELIX=<options> helix/pico:<keymap>)
+  $(info -    option= oled | back | under | na | no-ani)
+  $(info -             ios | sc | split-common | scan | verbose)
+  $(info -    ex.)
+  $(info -      make HELIX=oled     helix/pico:<keymap>)
+  $(info -      make HELIX=back     helix/pico:<keymap>)
+  $(info -      make HELIX=under    helix/pico:<keymap>)
+  $(info -      make HELIX=back,na  helix/pico:<keymap>)
+  $(info -      make HELIX=back,ios helix/pico:<keymap>)
+  $(info )
+endef
+
+  ifneq ($(strip $(HELIX)),)
+    COMMA=,
+    helix_option := $(subst $(COMMA), , $(HELIX))
+    ifneq ($(filter help,$(helix_option)),)
+      $(eval $(call HELIX_HELP_MSG))
+      $(error )
+    endif
+    ifneq ($(filter oled,$(helix_option)),)
+      OLED_ENABLE = yes
+    endif
+    ifneq ($(filter back,$(helix_option)),)
+      LED_BACK_ENABLE = yes
+    else ifneq ($(filter under,$(helix_option)),)
+      LED_UNDERGLOW_ENABLE = yes
+    endif
+    ifneq ($(filter na,$(helix_option)),)
+      LED_ANIMATIONS = no
+    endif
+    ifneq ($(filter no_ani,$(helix_option)),)
+      LED_ANIMATIONS = no
+    endif
+    ifneq ($(filter no-ani,$(helix_option)),)
+      LED_ANIMATIONS = no
+    endif
+    ifneq ($(filter ios,$(helix_option)),)
+      IOS_DEVICE_ENABLE = yes
+    endif
+    ifneq ($(filter sc,$(helix_option)),)
+      SPLIT_KEYBOARD = yes
+    endif
+    ifneq ($(filter split-common,$(helix_option)),)
+      SPLIT_KEYBOARD = yes
+    endif
+    ifneq ($(filter scan,$(helix_option)),)
+      # use DEBUG_MATRIX_SCAN_RATE
+      # see docs/newbs_testing_debugging.md
+      OPT_DEFS +=  -DDEBUG_MATRIX_SCAN_RATE
+      CONSOLE_ENABLE = yes
+      SHOW_VERBOSE_INFO = yes
+    endif
+    ifneq ($(filter verbose,$(helix_option)),)
+      SHOW_VERBOSE_INFO = yes
+    endif
+    SHOW_HELIX_OPTIONS = yes
+  endif
+
+ifneq ($(strip $(SPLIT_KEYBOARD)), yes)
+  SRC += local_drivers/serial.c
+  KEYBOARD_PATHS += $(HELIX_TOP_DIR)/local_drivers
+
+  # A workaround until #7089 is merged.
+  #   serial.c must not be compiled with the -lto option.
+  #   The current LIB_SRC has a side effect with the -fno-lto option, so use it.
+  LIB_SRC += local_drivers/serial.c
+
+  CUSTOM_MATRIX = yes
+
+  SRC += pico/matrix.c
+  SRC += pico/split_util.c
+endif
+
+########
+# convert Helix-specific options (that represent combinations of standard options)
+#   into QMK standard options.
+
+ifeq ($(strip $(LED_BACK_ENABLE)), yes)
+  RGBLIGHT_ENABLE = yes
+  OPT_DEFS += -DRGBLED_BACK
+  ifeq ($(strip $(LED_UNDERGLOW_ENABLE)), yes)
+    $(eval $(call HELIX_CUSTOMISE_MSG))
+    $(error LED_BACK_ENABLE and LED_UNDERGLOW_ENABLE both 'yes')
+  endif
+else ifeq ($(strip $(LED_UNDERGLOW_ENABLE)), yes)
+  RGBLIGHT_ENABLE = yes
+endif
+
+ifeq ($(strip $(IOS_DEVICE_ENABLE)), yes)
+    OPT_DEFS += -DIOS_DEVICE_ENABLE
+endif
+
+ifeq ($(strip $(LED_ANIMATIONS)), yes)
+    OPT_DEFS += -DLED_ANIMATIONS
+endif
+
+ifeq ($(strip $(OLED_ENABLE)), yes)
+    SRC += local_drivers/i2c.c
+    SRC += local_drivers/ssd1306.c
+    KEYBOARD_PATHS += $(HELIX_TOP_DIR)/local_drivers
+    OPT_DEFS += -DOLED_ENABLE
+    ifeq ($(strip $(LOCAL_GLCDFONT)), yes)
+        OPT_DEFS += -DLOCAL_GLCDFONT
+    endif
+endif
+
+ifeq ($(strip $(AUDIO_ENABLE)),yes)
+  ifeq ($(strip $(RGBLIGHT_ENABLE)),yes)
+    LTO_ENABLE = yes
+  endif
+  ifeq ($(strip $(OLED_ENABLE)),yes)
+    LTO_ENABLE = yes
+  endif
+endif
+
+ifneq ($(strip $(SHOW_HELIX_OPTIONS)),)
+  $(eval $(call HELIX_CUSTOMISE_MSG))
+  ifneq ($(strip $(SHOW_VERBOSE_INFO)),)
+     $(info -- RGBLIGHT_ENABLE    = $(RGBLIGHT_ENABLE))
+     $(info -- CONSOLE_ENABLE     = $(CONSOLE_ENABLE))
+     $(info -- OPT_DEFS           = $(OPT_DEFS))
+     $(info -- SPLIT_KEYBOARD     = $(SPLIT_KEYBOARD))
+     $(info -- LTO_ENABLE         = $(LTO_ENABLE))
+     $(info )
+  endif
+endif
+
+OLED_ENABLE = no # disable OLED in TOP/common_features.mk