Using gcc-4.8.1-1.fc19.x86_64 (but I've seen it with rhel6 gcc as well):

$ touch foo.c (works with a regular C program as well such as an hello world)
$ gcc -Wbadflag -c ./foo.c
gcc: error: unrecognized command line option '-Wbadflag'
$ gcc -Wno-badflag -c ./foo.c
$

$ echo '#warning foo' >>foo.c
$ gcc -Wno-badflag -c ./foo.c
./foo.c:1:2: warning: #warning foo [-Wcpp]
 #warning foo
  ^
cc1: warning: unrecognized command line option "-Wno-badflag" [enabled by default]

Expected result: -Wno-badflag and -Wbadflag gives the same result when they are used on a C file not producing any warnings (in this case, an empty foo.c).