libkrb5: disable optional tcl support

Avoid detection of host tcl headers.

The tcl package in Buildroot is not cross-compile safe. The generated
tclConfig.sh script has -L/usr/lib in TCL_LIB_SPEC.

Should fix:
http://autobuild.buildroot.net/results/d11/d118c3c09f6fc1de26491f2ed480ef28b091dba8/
http://autobuild.buildroot.net/results/035/0353e1443125da1e544d1a98348716bfe67c8726/

Cc: André Hentschel <nerv@dawncrow.de>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/libkrb5/libkrb5.mk

@@ -25,7 +25,8 @@ LIBKRB5_CONF_OPTS = \
 	--without-system-db \
 	--without-system-et \
 	--without-system-ss \
-	--without-system-verto
+	--without-system-verto \
+	--without-tcl
 
 ifeq ($(BR2_PACKAGE_OPENLDAP),y)
 LIBKRB5_CONF_OPTS += --with-ldap