update cray openmp compiler flag in advanced exercise makefile

advanced_lab/c/Makefile

 CC = cc
 ifeq ($(CRAY_PRGENVCRAY), loaded)
-CFLAGS = -O2 -homp
+CFLAGS = -O2 -openmp
 else ifeq ($(CRAY_PRGENVINTEL), loaded)
 CFLAGS = -O2 -openmp
 else ifeq ($(CRAY_PRGENVGNU), loaded)

advanced_lab/f90/Makefile

 FC = ftn
 ifeq ($(CRAY_PRGENVCRAY), loaded)
-FFLAGS = -O2 -homp
+FFLAGS = -O2 -openmp
 else ifeq ($(CRAY_PRGENVINTEL), loaded)
 FFLAGS = -O2 -openmp
 else ifeq ($(CRAY_PRGENVGNU), loaded)