Fix test guards

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/tests/suites/test_suite_x509write.function b/tests/suites/test_suite_x509write.function
index 84da143..2896a52 100644
--- a/tests/suites/test_suite_x509write.function
+++ b/tests/suites/test_suite_x509write.function
@@ -294,7 +294,7 @@
     TEST_ASSERT(mbedtls_pk_parse_keyfile(&issuer_key, issuer_key_file,
                                          issuer_pwd) == 0);
 
-#if defined(MBEDTLS_RSA_C)
+#if defined(MBEDTLS_RSA_C) && defined(MBEDTLS_PK_RSA_ALT_SUPPORT)
     /* For RSA PK contexts, create a copy as an alternative RSA context. */
     if (rsa_alt == 1 && mbedtls_pk_get_type(&issuer_key) == MBEDTLS_PK_RSA) {
         TEST_ASSERT(mbedtls_pk_setup_rsa_alt(&issuer_key_alt,