stmhal/Makefile: Drop use of -mabi=aapcs-linux; link libgcc by default.

The aapcs-linux ABI is not required, instead the default aapcs ABI is
enough.  And using the default ABI means that the provided libgcc will now
link with the firmware without warnings about variable vs fixed enums.

Although the binary size increases by about 1k, RAM usage is slightly
decreased.  And libgcc may prove useful in the future for things like
long-long division.

stmhal/Makefile

@@ -51,7 +51,7 @@ INC += -I../lib/mp-readline
 INC += -I../lib/netutils
 INC += -I../lib/timeutils
 
-CFLAGS_CORTEX_M = -mthumb -mabi=aapcs-linux -mfpu=fpv4-sp-d16 -mfloat-abi=hard -fsingle-precision-constant -Wdouble-promotion
+CFLAGS_CORTEX_M = -mthumb -mfpu=fpv4-sp-d16 -mfloat-abi=hard -fsingle-precision-constant -Wdouble-promotion
 CFLAGS_MCU_f4 = $(CFLAGS_CORTEX_M) -mtune=cortex-m4 -mcpu=cortex-m4 -DMCU_SERIES_F4
 CFLAGS_MCU_f7 = $(CFLAGS_CORTEX_M) -mtune=cortex-m7 -mcpu=cortex-m7 -DMCU_SERIES_F7
 CFLAGS_MCU_l4 = $(CFLAGS_CORTEX_M) -mtune=cortex-m4 -mcpu=cortex-m4 -DMCU_SERIES_L4
@@ -64,7 +64,7 @@ CFLAGS += -Iboards/$(BOARD)
 CFLAGS += -DSTM32_HAL_H='<stm32$(MCU_SERIES)xx_hal.h>'
 
 LDFLAGS = -nostdlib -L $(LD_DIR) -T $(LD_FILE) -Map=$(@:.elf=.map) --cref
-LIBS =
+LIBS = $(shell $(CC) $(CFLAGS) -print-libgcc-file-name)
 
 # Remove uncalled code from the final image.
 CFLAGS += -fdata-sections -ffunction-sections
@@ -78,9 +78,6 @@ else
 COPT += -Os -DNDEBUG
 endif
 
-# uncomment this if you want libgcc
-#LIBS += $(shell $(CC) $(CFLAGS) -print-libgcc-file-name)
-
 SRC_LIB = $(addprefix lib/,\
 	libc/string0.c \
 	libm/math.c \