Refactor quantum/split_common/i2c.c, quantum/split_common/serial.c (#4522)

* add temporary compile test shell script

* Extended support of SKIP_VERSION to make invariant compile results during testing.

* build_keyboard.mk, tmk_core/rules.mk: add LIB_SRC, QUANTUM_LIB_SRC support

Support compiled object enclosed in library.

e.g.
```
LIB_SRC += xxxx.c
xxxx.c --> xxxx.o ---> xxxx.a
```

* remove 'ifdef/ifndef USE_I2C' from quantum/split_common/{i2c|serial}.c

* add SKIP_DEBUG_INFO into tmk_core/rules.mk

When SKIP_DEBUG_INFO=yes is specified, do not use the -g option at compile time.

* tmk_core/rules.mk: Library object need -fno-lto

* add SKIP_DEBUG_INFO=yes

* remove temporary compile test shell script

* add '#define SOFT_SERIAL_PIN D0' to keyboards/lets_split/rev?/config.h

* quantum/split_common/serial.c: Changed not to use USE_I2C.

1 files changed, 6 insertions, 0 deletions

diff --git a/build_keyboard.mk b/build_keyboard.mk
index d225fe821..b639b92d3 100644
--- a/build_keyboard.mk
+++ b/build_keyboard.mk
@@ -34,6 +34,10 @@ $(error MASTER does not have a valid value(left/right))
     endif
 endif
 
+ifdef SKIP_VERSION
+    OPT_DEFS += -DSKIP_VERSION
+endif
+
 # Determine which subfolders exist.
 KEYBOARD_FOLDER_PATH_1 := $(KEYBOARD)
 KEYBOARD_FOLDER_PATH_2 := $(patsubst %/,%,$(dir $(KEYBOARD_FOLDER_PATH_1)))
@@ -278,6 +282,7 @@ ifneq ("$(wildcard $(KEYMAP_PATH)/config.h)","")
 endif
 
 # # project specific files
+SRC += $(patsubst %.c,%.clib,$(LIB_SRC))
 SRC += $(KEYBOARD_SRC) \
     $(KEYMAP_C) \
     $(QUANTUM_SRC)
@@ -296,6 +301,7 @@ include $(TMK_PATH)/protocol.mk
 include $(TMK_PATH)/common.mk
 include bootloader.mk
 
+SRC += $(patsubst %.c,%.clib,$(QUANTUM_LIB_SRC))
 SRC += $(TMK_COMMON_SRC)
 OPT_DEFS += $(TMK_COMMON_DEFS)
 EXTRALDFLAGS += $(TMK_COMMON_LDFLAGS)