use libgcrypt for MD5

This makes sure that CHAP authentication is disabled if the system
is running in FIPS 140-2 mode.  MD5 is not a secure algorithm according
to the standard.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure.ac

@@ -18,6 +18,9 @@ AC_SUBST(WARN_CFLAGS)
 
 AC_CONFIG_HEADER(config.h)
 
+AC_CHECK_LIB([gcrypt], [gcry_control])
+AM_CONDITIONAL([HAVE_LIBGCRYPT], [test $ac_cv_lib_gcrypt_gcry_control = yes])
+
 AC_CACHE_CHECK([for sin_len in sock],libiscsi_cv_HAVE_SOCK_SIN_LEN,[
 AC_TRY_COMPILE([#include <sys/types.h>
 #include <sys/socket.h>