Do not define CC and CXX in sdk/cpprt/Makefile

This will prevent the cross compilation environment from defining its
own CC and CXX.

Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

sdk/cpprt/Makefile

@@ -79,9 +79,6 @@ $(CPPRT): $(OBJS) prepare-libunwind libunwind
 	$(CP) linux/libunwind/src/.libs/libunwind.a $(CPPRT)
 	$(AR) rs $@ $(OBJS)
 
-$(CPPRT): CC  = gcc
-$(CPPRT): CXX = g++
-
 .PHONY: libunwind
 libunwind:
 	cd linux/libunwind/ && ( test -f Makefile || ./autogen-linux.sh ) && $(MAKE) -j5