ECDSA requires a short Weierstrass curve

Document in config.h, and enforce in check_config.h, that
MBEDTLS_ECDSA_C requires at least one short Weierstrass curve to be
enabled. A Montgomery curve is not enough.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h
index f2148a8..3596597 100644
--- a/include/mbedtls/check_config.h
+++ b/include/mbedtls/check_config.h
@@ -103,6 +103,17 @@
 
 #if defined(MBEDTLS_ECDSA_C) &&            \
     ( !defined(MBEDTLS_ECP_C) ||           \
+      !( defined(MBEDTLS_ECP_DP_SECP192R1_ENABLED) || \
+         defined(MBEDTLS_ECP_DP_SECP224R1_ENABLED) || \
+         defined(MBEDTLS_ECP_DP_SECP256R1_ENABLED) || \
+         defined(MBEDTLS_ECP_DP_SECP384R1_ENABLED) || \
+         defined(MBEDTLS_ECP_DP_SECP521R1_ENABLED) || \
+         defined(MBEDTLS_ECP_DP_SECP192K1_ENABLED) || \
+         defined(MBEDTLS_ECP_DP_SECP224K1_ENABLED) || \
+         defined(MBEDTLS_ECP_DP_SECP256K1_ENABLED) || \
+         defined(MBEDTLS_ECP_DP_BP256R1_ENABLED) ||   \
+         defined(MBEDTLS_ECP_DP_BP384R1_ENABLED) ||   \
+         defined(MBEDTLS_ECP_DP_BP512R1_ENABLED) ) || \
       !defined(MBEDTLS_ASN1_PARSE_C) ||    \
       !defined(MBEDTLS_ASN1_WRITE_C) )
 #error "MBEDTLS_ECDSA_C defined, but not all prerequisites"