gcc -c -o main.o main.c -Wall -Wextra
main.c:42:10: error: 'foo' undeclared (first use in this function)
main.c:42:10: note: each undeclared identifier is reported only once for each function it appears in
main.c:55:5: warning: unused variable 'x' [-Wunused-variable]
main.c:3:10: fatal error: missing_header.h: No such file or directory
compilation terminated.
make: *** [Makefile:15: main.o] Error 1
