ports/{bare-arm,minimal}/Makefile: Only build with core source files.

These ports don't need anything from extmod so don't include those files
at all in the build.  This speeds up the build by about 10% when building
with a single core.

ports/bare-arm/Makefile

@@ -36,7 +36,7 @@ SRC_S = \
 #	startup_stm32f40xx.s \
 	gchelper.s \
 
-OBJ = $(PY_O) $(addprefix $(BUILD)/, $(SRC_C:.c=.o) $(SRC_S:.s=.o))
+OBJ = $(PY_CORE_O) $(addprefix $(BUILD)/, $(SRC_C:.c=.o) $(SRC_S:.s=.o))
 
 all: $(BUILD)/firmware.elf
 

ports/minimal/Makefile

@@ -47,7 +47,7 @@ SRC_C = \
 	lib/mp-readline/readline.c \
 	$(BUILD)/_frozen_mpy.c \
 
-OBJ = $(PY_O) $(addprefix $(BUILD)/, $(SRC_C:.c=.o))
+OBJ = $(PY_CORE_O) $(addprefix $(BUILD)/, $(SRC_C:.c=.o))
 
 ifeq ($(CROSS), 1)
 all: $(BUILD)/firmware.dfu