build common .o files everywhere (fixes issue #29)

vector.o, nvic.o, scb.o and assert.o are available on every platform,
but at least some of them differ between the implementations. they
already got built explicityly on some platforms; now adding them to the
common Makefile.include.

lib/stm32/f4/Makefile

@@ -29,10 +29,9 @@ CFLAGS		= -Os -g -Wall -Wextra -I../../../include -fno-common \
 		  -ffunction-sections -fdata-sections -MD -DSTM32F4
 # ARFLAGS	= rcsv
 ARFLAGS		= rcs
-OBJS		= vector.o rcc.o gpio.o usart.o spi.o flash.o nvic.o \
-		  i2c.o systick.o exti.o scb.o pwr.o timer.o \
-		  usb.o usb_standard.o usb_control.o usb_f107.o \
-		  assert.o
+OBJS		= rcc.o gpio.o usart.o spi.o flash.o nvic.o \
+		  i2c.o exti.o pwr.o timer.o \
+		  usb.o usb_standard.o usb_control.o usb_f107.o
 
 VPATH += ../../usb:../:../../cm3