Add NO_CRYPT to fix build with glibc 2.28

Since glibc 2.28
(https://savannah.gnu.org/forum/forum.php?forum_id=9205), the obsolete
functions encrypt, encrypt_r, setkey, setkey_r, cbc_crypt, ecb_crypt,
and des_setparity are no longer available to newly linked binaries, and
the headers <rpc/des_crypt.h> and <rpc/rpc_des.h> are no longer
installed. These functions encrypted and decrypted data with the DES
block cipher, which is no longer considered secure. Software that still
uses these functions should switch to a modern cryptography library,
such as libgcrypt.

So add a NO_CRYPT variable to disable test/crypt

Fixes:
 - http://autobuild.buildroot.org/results/158438debb0ce313b012b871e199bed42ba38294

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

test/Makefile

@@ -39,6 +39,10 @@ ifeq ($(NO_MATH),1)
 DIRS := $(filter-out math,$(DIRS))
 endif
 
+ifeq ($(NO_CRYPT),1)
+DIRS := $(filter-out crypt,$(DIRS))
+endif
+
 test check all: run
 
 run: subdirs_run