hash: allow non-security MD5 use in FIPS mode

gnutls running in the FIPS140-2 mode does not allow MD5 to be
initialized, which breaks chronyd using MD5 to calculate reference ID
of IPv6 addresses. Specify a new hash algorithm for non-security MD5 use
and temporarily switch to the lax mode when initializing the hash
function.

hash_tomcrypt.c

@@ -71,6 +71,9 @@ HSH_GetHashId(HSH_Algorithm algorithm)
 {
   int i, h;
 
+  if (algorithm == HSH_MD5_NONCRYPTO)
+    algorithm = HSH_MD5;
+
   for (i = 0; hashes[i].algorithm != 0; i++) {
     if (hashes[i].algorithm == algorithm)
       break;