-xM1

Collects dependencies like -xM, but excludes /usr/include files. For example:

more hello.c
#include<stdio.h>
main()
{
 (void)printf("hello\n");
}
cc -xM hello.c
hello.o: hello.c
hello.o: /usr/include/stdio.h

Compiling with -xM1 does not report header file dependencies:

cc -xM1 hello.c
hello.o: hello.c