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
POLARSSL_PEM_PARSE_C.
diff --git a/ChangeLog b/ChangeLog
index d4cf85b..08f705e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,12 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
+= mbed TLS x.x.x branch xxxx-xx-xx
+
+Bugfix
+   * 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 POLARSSL_PEM_PARSE_C. #562
+
 = mbed TLS 1.3.18 branch 2016-10-17
 
 Security