What does make[number] mean in make V=s

The error you're encountering:

*** missing separator (did you mean TAB instead of 8 spaces?). Stop.

Means that the makefile contains spaces instead of Tab's. The make utility is notoriously picky about the use of Space instead of Tab. So it's likely that the makefile contains Space at the beginning of rule stanzas within the file.

Example

Let's say I have the following 3 .c files:

char *
hello() 
{
  return "Hello";
}

char *
world() 
{
  return "world";
}

#include <stdio.h>

/* Prototypes. */
char *hello();
char *world();

int
main(int argc, char *argv[]) 
{
    printf("%s, %s!\n", hello(), world());
    return 0;
}    

Say I have the following Makefile:

# The executable 'helloworld' depends on all 3 object files
helloworld: main.o hello.o world.o
        cc -o helloworld main.o hello.o world.o # Line starts with TAB!

# Build main.o (only requires main.c to exist)
main.o: main.c
        cc -c main.c # Line starts with TAB!

# Build hello.o (only requires hello.c to exist)
hello.o: hello.c
        cc -c hello.c # Line starts with TAB!

# Build world.o (only requires world.c to exist)
world.o: world.c
        cc -c world.c # Line starts with TAB!

#  Remove object files, executables (UNIX/Windows), Emacs backup files, 
#+ and core files
clean:
        rm -rf  *.o helloworld *~ *.core core # Line starts with TAB!

Now we try to build a target

When I run it against the target helloworld:

$ make helloworld
makefile:3: *** missing separator (did you mean TAB instead of 8 spaces?).  Stop.

Look familiar?

Fixing the issue

You can fix this by changing the Spaces to actual Tab characters. I used vim to repair my file. Simply open it:

$ vim makefile

And then run this command within:

:%s/^[ ]\+/^I/

NOTE: ^I is a special character. Typing ^ followed by I will be interpreted differently compared to Ctrl+V-Ctrl+I.

This will substitute all the lines that begin with 1 or more Spaces with an actual Tab.

Now when I rerun my helloworld target:

$ make helloworld
cc -c main.c # Line starts with TAB!
cc -c hello.c # Line starts with TAB!
cc -c world.c # Line starts with TAB!
cc -o helloworld main.o hello.o world.o # Line starts with TAB!

References

• Makefile for hello.c, world.c, and main.c

I'm pretty sure that there is no way to disable GNU make extensions. The .POSIX target improves the compatibility but does not disable compatible extensions such as functions, proprietary dot targets, % patterns in targets, etc.

I don't know of any make implementation that sticks to POSIX features. For example MINIX, Solaris, OpenBSD all have their own extensions. You could at least try to build your programs with these four implementations (assuming that your programs do build on all these platforms), which will give you a pretty good portability assurance in practice. Add Windows with the make utility from Visual Studio, plus a port of some Unix shell tools, if you can use a non-free OS (I think there's a free version of VS that would be enough).