lguest: clean up example launcher compile flags.

18 months ago 5bbf89fc changed to loading
bzImages directly, and no longer manually ungzipping them, so we no longer
need libz.

Also, -m32 is useful for those on 64-bit platforms (and harmless on
32-bit).
Reported-by: Ron Minnich <rminnich@gmail.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Documentation/lguest/Makefile

 # This creates the demonstration utility "lguest" which runs a Linux guest.
-CFLAGS:=-Wall -Wmissing-declarations -Wmissing-prototypes -O3 -I../../include -I../../arch/x86/include -U_FORTIFY_SOURCE
-LDLIBS:=-lz
+CFLAGS:=-m32 -Wall -Wmissing-declarations -Wmissing-prototypes -O3 -I../../include -I../../arch/x86/include -U_FORTIFY_SOURCE
 
 all: lguest