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.

ChangeLog

@@ -5,6 +5,9 @@ mbed TLS ChangeLog (Sorted per branch, date)
 Bugfix
    * Fix redefinition of macro ssl_set_bio to undefined symbol
      mbedtls_ssl_set_bio_timeout in compat-1.3.h. #673
+   * Fix unused variable/function compilation warnings in pem.c and x509_csr.c
+     that are reported when building mbed TLS with a config.h that does not
+     define MBEDTLS_PEM_PARSE_C. #562
    * Fixed multiple buffer overreads in mbedtls_pem_read_buffer() when parsing
      the input string in PEM format to extract the different components. Found
      by Eyal Itkin.

library/pem.c

@@ -44,12 +44,12 @@
 #define mbedtls_free       free
 #endif
 
+#if defined(MBEDTLS_PEM_PARSE_C)
 /* Implementation that should never be optimized out by the compiler */
 static void mbedtls_zeroize( void *v, size_t n ) {
     volatile unsigned char *p = v; while( n-- ) *p++ = 0;
 }
 
-#if defined(MBEDTLS_PEM_PARSE_C)
 void mbedtls_pem_init( mbedtls_pem_context *ctx )
 {
     memset( ctx, 0, sizeof( mbedtls_pem_context ) );

library/x509_csr.c

@@ -259,8 +259,8 @@ int mbedtls_x509_csr_parse_der( mbedtls_x509_csr *csr,
  */
 int mbedtls_x509_csr_parse( mbedtls_x509_csr *csr, const unsigned char *buf, size_t buflen )
 {
-    int ret;
 #if defined(MBEDTLS_PEM_PARSE_C)
+    int ret;
     size_t use_len;
     mbedtls_pem_context pem;
 #endif