Build the geom_uncompress(4) module by default.

Fix geom_uncompress(4) module loading.  Don't link zlib.c (which is a module
itself) directly.

The built module was verified and used to read a few mkulzma(8) images on
amd64 to validate some of the informations on the manual page.

While here, don't overwrite CFLAGS.

Reviewed by:	ray
Approved by:	adrian (mentor)

sys/geom/uncompress/g_uncompress.c

@@ -664,4 +664,4 @@ static struct g_class g_uncompress_class = {
 };
 
 DECLARE_GEOM_CLASS(g_uncompress_class, g_uncompress);
-
+MODULE_DEPEND(g_uncompress, zlib, 1, 1, 1);

sys/modules/geom/Makefile

@@ -24,6 +24,7 @@ SUBDIR=	geom_bde \
 	geom_shsec \
 	geom_stripe \
 	geom_sunlabel \
+	geom_uncompress \
 	geom_uzip \
 	geom_vinum \
 	geom_virstor \

sys/modules/geom/geom_uncompress/Makefile

@@ -7,11 +7,11 @@
     ${.CURDIR}/../../../net
 
 KMOD=	geom_uncompress
-CFLAGS= -I${.CURDIR}/../../../geom/uncompress/ \
+CFLAGS+= -I${.CURDIR}/../../../geom/uncompress/ \
 	-I${.CURDIR}/../../../contrib/xz-embedded/freebsd \
 	-I${.CURDIR}/../../../contrib/xz-embedded/linux/lib/xz/
 SRCS=	g_uncompress.c xz_crc32.c xz_dec_bcj.c xz_dec_lzma2.c xz_dec_stream.c \
-    xz_malloc.c zlib.c
+    xz_malloc.c
 SRCS+=	xz.h xz_config.h xz_lzma2.h xz_malloc.h xz_private.h xz_stream.h zlib.h
 
 .include <bsd.kmod.mk>