help text: do not report the insanly long list of Warning flags.

help text: do not report the insanly long list of Warning flags.

Originally there was just one. Now that XCB has been integrated with X and
uses the same compiler flags, it is a different story.

  Used CFLAGS:
    CPPFLAGS............:
    CFLAGS..............: -g -O2
    Warning CFLAGS......:  -Wall -Wpointer-arith AND SO ON FOR 8 lines...

It completely defaces the otherwise excellent output.

Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Gaetan Nadon <memsize@videotron.ca>
Signed-off-by: Uli Schlachter <psychon@znc.in>