conditionaly compile ECDH and ECDSA alt functions

Return the condition compilation flags surrounding
`mbedtls_ecdh_compute_shared()`, `mbedtls_ecdh_gen_public()`,
`mbedtls_ecdsa_sign()` and `mbedtls_ecdsa_verify()` that were accidentally
removed in a previous merge.
Resolves #2163

library/ecdh.c

@@ -110,7 +110,6 @@ cleanup:
 
     return( ret );
 }
-#endif /* MBEDTLS_ECDH_COMPUTE_SHARED_ALT */
 
 /*
  * Compute shared secret (SEC1 3.3.1)
@@ -123,6 +122,7 @@ int mbedtls_ecdh_compute_shared( mbedtls_ecp_group *grp, mbedtls_mpi *z,
     return( ecdh_compute_shared_restartable( grp, z, Q, d,
                                              f_rng, p_rng, NULL ) );
 }
+#endif /* MBEDTLS_ECDH_COMPUTE_SHARED_ALT */
 
 /*
  * Initialize context
@@ -201,9 +201,16 @@ int mbedtls_ecdh_make_params( mbedtls_ecdh_context *ctx, size_t *olen,
         rs_ctx = &ctx->rs;
 #endif
 
+
+#if defined(MBEDTLS_ECDH_GEN_PUBLIC_ALT)
+    if( ( ret = mbedtls_ecdh_gen_public( &ctx->grp, &ctx->d, &ctx->Q,
+                                         f_rng, p_rng ) ) != 0 )
+        return( ret );
+#else
     if( ( ret = ecdh_gen_public_restartable( &ctx->grp, &ctx->d, &ctx->Q,
                                              f_rng, p_rng, rs_ctx ) ) != 0 )
         return( ret );
+#endif
 
     if( ( ret = mbedtls_ecp_tls_write_group( &ctx->grp, &grp_len, buf, blen ) )
                 != 0 )
@@ -287,9 +294,15 @@ int mbedtls_ecdh_make_public( mbedtls_ecdh_context *ctx, size_t *olen,
         rs_ctx = &ctx->rs;
 #endif
 
+#if defined(MBEDTLS_ECDH_GEN_PUBLIC_ALT)
+    if( ( ret = mbedtls_ecdh_gen_public( &ctx->grp, &ctx->d, &ctx->Q,
+                                         f_rng, p_rng ) ) != 0 )
+        return( ret );
+#else
     if( ( ret = ecdh_gen_public_restartable( &ctx->grp, &ctx->d, &ctx->Q,
                     f_rng, p_rng, rs_ctx ) ) != 0 )
         return( ret );
+#endif
 
     return mbedtls_ecp_tls_write_point( &ctx->grp, &ctx->Q, ctx->point_format,
                                 olen, buf, blen );
@@ -335,11 +348,19 @@ int mbedtls_ecdh_calc_secret( mbedtls_ecdh_context *ctx, size_t *olen,
         rs_ctx = &ctx->rs;
 #endif
 
+#if defined(MBEDTLS_ECDH_COMPUTE_SHARED_ALT)
+    if( ( ret = mbedtls_ecdh_compute_shared( &ctx->grp, &ctx->z, &ctx->Qp,
+                                             &ctx->d, f_rng, p_rng ) ) != 0 )
+    {
+        return( ret );
+    }
+#else
     if( ( ret = ecdh_compute_shared_restartable( &ctx->grp,
                     &ctx->z, &ctx->Qp, &ctx->d, f_rng, p_rng, rs_ctx ) ) != 0 )
     {
         return( ret );
     }
+#endif
 
     if( mbedtls_mpi_size( &ctx->z ) > blen )
         return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );

library/ecdsa.c

@@ -237,7 +237,6 @@ cleanup:
     return( ret );
 }
 
-#if !defined(MBEDTLS_ECDSA_SIGN_ALT)
 /*
  * Compute ECDSA signature of a hashed message (SEC1 4.1.3)
  * Obviously, compared to SEC1 4.1.3, we skip step 4 (hash message)
@@ -369,8 +368,8 @@ cleanup:
 
     return( ret );
 }
-#endif /* MBEDTLS_ECDSA_SIGN_ALT */
 
+#if !defined(MBEDTLS_ECDSA_SIGN_ALT)
 /*
  * Compute ECDSA signature of a hashed message
  */
@@ -381,6 +380,7 @@ int mbedtls_ecdsa_sign( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s,
     return( ecdsa_sign_restartable( grp, r, s, d, buf, blen,
                                     f_rng, p_rng, NULL ) );
 }
+#endif /* MBEDTLS_ECDSA_SIGN_ALT */
 
 #if defined(MBEDTLS_ECDSA_DETERMINISTIC)
 /*
@@ -432,8 +432,13 @@ static int ecdsa_sign_det_restartable( mbedtls_ecp_group *grp,
 
 sign:
 #endif
+#if defined(MBEDTLS_ECDSA_SIGN_ALT)
+    ret = mbedtls_ecdsa_sign( grp, r, s, d, buf, blen,
+                              mbedtls_hmac_drbg_random, p_rng );
+#else
     ret = ecdsa_sign_restartable( grp, r, s, d, buf, blen,
                       mbedtls_hmac_drbg_random, p_rng, rs_ctx );
+#endif
 
 cleanup:
     mbedtls_hmac_drbg_free( &rng_ctx );
@@ -455,7 +460,6 @@ int mbedtls_ecdsa_sign_det( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi
 }
 #endif /* MBEDTLS_ECDSA_DETERMINISTIC */
 
-#if !defined(MBEDTLS_ECDSA_VERIFY_ALT)
 /*
  * Verify ECDSA signature of hashed message (SEC1 4.1.4)
  * Obviously, compared to SEC1 4.1.3, we skip step 2 (hash message)
@@ -564,8 +568,8 @@ cleanup:
 
     return( ret );
 }
-#endif /* MBEDTLS_ECDSA_VERIFY_ALT */
 
+#if !defined(MBEDTLS_ECDSA_VERIFY_ALT)
 /*
  * Verify ECDSA signature of hashed message
  */
@@ -575,6 +579,7 @@ int mbedtls_ecdsa_verify( mbedtls_ecp_group *grp,
 {
     return( ecdsa_verify_restartable( grp, buf, blen, Q, r, s, NULL ) );
 }
+#endif /* MBEDTLS_ECDSA_VERIFY_ALT */
 
 /*
  * Convert a signature (given by context) to ASN.1
@@ -626,8 +631,13 @@ int mbedtls_ecdsa_write_signature_restartable( mbedtls_ecdsa_context *ctx,
 #else
     (void) md_alg;
 
+#if defined(MBEDTLS_ECDSA_SIGN_ALT)
+    MBEDTLS_MPI_CHK( mbedtls_ecdsa_sign( &ctx->grp, &r, &s, &ctx->d,
+                         hash, hlen, f_rng, p_rng ) );
+#else
     MBEDTLS_MPI_CHK( ecdsa_sign_restartable( &ctx->grp, &r, &s, &ctx->d,
                          hash, hlen, f_rng, p_rng, rs_ctx ) );
+#endif
 #endif
 
     MBEDTLS_MPI_CHK( ecdsa_signature_to_asn1( &r, &s, sig, slen ) );
@@ -712,10 +722,15 @@ int mbedtls_ecdsa_read_signature_restartable( mbedtls_ecdsa_context *ctx,
         ret += MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
         goto cleanup;
     }
-
+#if defined(MBEDTLS_ECDSA_VERIFY_ALT)
+    if( ( ret = mbedtls_ecdsa_verify( &ctx->grp, hash, hlen,
+                                      &ctx->Q, &r, &s ) ) != 0 )
+        goto cleanup;
+#else
     if( ( ret = ecdsa_verify_restartable( &ctx->grp, hash, hlen,
                               &ctx->Q, &r, &s, rs_ctx ) ) != 0 )
         goto cleanup;
+#endif
 
     /* At this point we know that the buffer starts with a valid signature.
      * Return 0 if the buffer just contains the signature, and a specific