Makefile does not work with gnu make

[mghansen256]

When using gnu make, I have to change line 50 in Grbl9fMega2560/Makefile from
.c.o:
to
%.o: %.cpp
Otherwise, compilation does not work, because the wrong c++ compiler is used, error message below. For which make program is the supplied Makefile?

Best regards,

Michael

Error message:
g++ -c -o main.o main.cpp
In file included from main.cpp:22:0:
system.h:25:20: fatal error: avr/io.h: No such file or directory
#include <avr/io.h>
^
compilation terminated.
: recipe for target 'main.o' failed
make: *** [main.o] Error 1