Use correct test case conditionals for helper functions in tests/suites

Fix unused-function errors.

Signed-off-by: Michael Schuster <michael@schuster.ms>
diff --git a/tests/suites/test_suite_x509write.function b/tests/suites/test_suite_x509write.function
index 901a88a..2762b0f 100644
--- a/tests/suites/test_suite_x509write.function
+++ b/tests/suites/test_suite_x509write.function
@@ -10,7 +10,11 @@
 #include "mbedtls/pk.h"
 #include "mbedtls/psa_util.h"
 
-#if defined(MBEDTLS_RSA_C)
+#if defined(MBEDTLS_PEM_WRITE_C) && \
+    defined(MBEDTLS_X509_CRT_WRITE_C) && \
+    defined(MBEDTLS_X509_CRT_PARSE_C) && \
+    defined(MBEDTLS_MD_CAN_SHA1) && \
+    defined(MBEDTLS_RSA_C) && defined(MBEDTLS_PK_RSA_ALT_SUPPORT)
 static int mbedtls_rsa_decrypt_func(void *ctx, size_t *olen,
                                     const unsigned char *input, unsigned char *output,
                                     size_t output_max_len)
@@ -30,7 +34,7 @@
 {
     return ((const mbedtls_rsa_context *) ctx)->len;
 }
-#endif /* MBEDTLS_RSA_C */
+#endif
 
 #if defined(MBEDTLS_USE_PSA_CRYPTO) && \
     defined(MBEDTLS_PEM_WRITE_C) && defined(MBEDTLS_X509_CSR_WRITE_C)