Add assert macros to aid in debugging.

Adds libopencm3/cm3/assert.h header that provides assertion check macros
similar to those provided by the standard C library.

Thanks to Nicolas Schodet for help.

lib/lpc43xx/Makefile

@@ -31,8 +31,9 @@ CFLAGS		= -O2 -g3 -Wall -Wextra -I../../include -fno-common \
 		  -mfloat-abi=hard -mfpu=fpv4-sp-d16
 # ARFLAGS	= rcsv
 ARFLAGS		= rcs
-OBJS		= gpio.o vector.o scu.o i2c.o ssp.o nvic.o systick.o
+OBJS		= gpio.o vector.o scu.o i2c.o ssp.o nvic.o systick.o \
+		  assert.o
 
-# VPATH += ../usb
+VPATH += ../cm3
 
 include ../Makefile.include