Replace Werror removal with pragma

Signed-off-by: Ben Taylor <ben.taylor@linaro.org>

library/ssl_tls12_client.c

@@ -19,6 +19,7 @@
 
 #include "psa_util_internal.h"
 #include "psa/crypto.h"
+#pragma GCC diagnostic warning "-Wenum-conversion"
 #if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
 /* Define a local translating function to save code size by not using too many
  * arguments in each translating place. */

library/ssl_tls13_generic.c

@@ -25,6 +25,7 @@
 
 #include "psa/crypto.h"
 #include "psa_util_internal.h"
+#pragma GCC diagnostic warning "-Wenum-conversion"
 
 #if defined(MBEDTLS_SSL_TLS1_3_KEY_EXCHANGE_MODE_SOME_EPHEMERAL_ENABLED)
 /* Define a local translating function to save code size by not using too many

library/x509_crt.c

@@ -17,6 +17,8 @@
  *  [SIRO] https://cabforum.org/wp-content/uploads/Chunghwatelecom201503cabforumV4.pdf
  */
 
+#pragma GCC diagnostic warning "-Wenum-conversion"
+
 #include "x509_internal.h"
 
 #if defined(MBEDTLS_X509_CRT_PARSE_C)