So uhhh, I don't have a makefile? and I also don't know how to generate one.
Aside from the code above the instructions read
Make sure your current directory is where your test_1.S file is and type the following:
arm-elf-gcc -mthumb-interwork -specs=gba.specs f.S and hit enter.
arm-elf-objcopy -O binary a.out a.gba and hit enter (not gonna say that again).
If no errors are generated, a "a.gba" file will be, run it. It should make a fairly red(ish) screen. Don't worry about understanding the code right now, this is just to make sure you can compile some code.
The problem is that those particular instructions don't actually do anything, it just reads it as a bad command, possibly because it was written for an older version of DevkitARM, I saw a post somewhere that said I should just use the make command.