cc/gcc: add option to use system zlib

In some cases, it might be desirable to use the system zlib

Eg. because latest gcc seem to be totally borked when it comes
to multilib, and tries to build a multilib host zlib, when it
is *absolutely* *not* needed: we want mulitlib on the target,
not on the host! Sigh... :-(

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

diff -dur ELFkickers.orig/sstrip/Makefile ELFkickers/sstrip/Makefile

--- ELFkickers.orig/sstrip/Makefile	2001-03-24 12:58:27.000000000 +0100

+++ ELFkickers/sstrip/Makefile	2007-05-31 21:17:18.000000000 +0200

@@ -1,7 +1,7 @@

 #  Makefile for sstrip

 sstrip: sstrip.c

-	gcc -ggdb -Wall -W -o sstrip sstrip.c

+	$(CC) -Wall -W -o sstrip sstrip.c

 clean:

 	rm -f sstrip