Fix unused variable/function compilation warnings

This PR fixes a number of unused variable/function compilation warnings
that arise when using a config.h that does not define the macro
MBEDTLS_PEM_PARSE_C.
diff --git a/library/x509_crt.c b/library/x509_crt.c
index 80af725..056dc16 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -969,8 +969,8 @@
  */
 int mbedtls_x509_crt_parse( mbedtls_x509_crt *chain, const unsigned char *buf, size_t buflen )
 {
-    int success = 0, first_error = 0, total_failed = 0;
 #if defined(MBEDTLS_PEM_PARSE_C)
+    int success = 0, first_error = 0, total_failed = 0;
     int buf_format = MBEDTLS_X509_FORMAT_DER;
 #endif