Check libssl function returns

Mark most functions returning a result defined in any libssl header file
with __owur to warn if they are used without checking the return value.
Use -DUNUSED_RETURN compiler flag with gcc to activate these warnings.
Some functions returning a result are skipped if it is common and valid to
use these functions without checking the return value.
Reviewed-by: NRichard Levitte <levitte@openssl.org>

ssl/srtp.h

@@ -132,11 +132,11 @@ extern "C" {
 
 # ifndef OPENSSL_NO_SRTP
 
-int SSL_CTX_set_tlsext_use_srtp(SSL_CTX *ctx, const char *profiles);
-int SSL_set_tlsext_use_srtp(SSL *ctx, const char *profiles);
+__owur int SSL_CTX_set_tlsext_use_srtp(SSL_CTX *ctx, const char *profiles);
+__owur int SSL_set_tlsext_use_srtp(SSL *ctx, const char *profiles);
 
-STACK_OF(SRTP_PROTECTION_PROFILE) *SSL_get_srtp_profiles(SSL *ssl);
-SRTP_PROTECTION_PROFILE *SSL_get_selected_srtp_profile(SSL *s);
+__owur STACK_OF(SRTP_PROTECTION_PROFILE) *SSL_get_srtp_profiles(SSL *ssl);
+__owur SRTP_PROTECTION_PROFILE *SSL_get_selected_srtp_profile(SSL *s);
 
 # endif
 

ssl/tls1.h

@@ -312,8 +312,8 @@ extern "C" {
 
 #  define TLSEXT_MAXLEN_host_name 255
 
-const char *SSL_get_servername(const SSL *s, const int type);
-int SSL_get_servername_type(const SSL *s);
+__owur const char *SSL_get_servername(const SSL *s, const int type);
+__owur int SSL_get_servername_type(const SSL *s);
 /*
  * SSL_export_keying_material exports a value derived from the master secret,
  * as specified in RFC 5705. It writes |olen| bytes to |out| given a label and
@@ -321,7 +321,7 @@ int SSL_get_servername_type(const SSL *s);
  * flag controls whether a context is included.) It returns 1 on success and
  * zero otherwise.
  */
-int SSL_export_keying_material(SSL *s, unsigned char *out, size_t olen,
+__owur int SSL_export_keying_material(SSL *s, unsigned char *out, size_t olen,
                                const char *label, size_t llen,
                                const unsigned char *p, size_t plen,
                                int use_context);
@@ -334,7 +334,7 @@ int SSL_get_shared_sigalgs(SSL *s, int idx,
                            int *psign, int *phash, int *psignandhash,
                            unsigned char *rsig, unsigned char *rhash);
 
-int SSL_check_chain(SSL *s, X509 *x, EVP_PKEY *pk, STACK_OF(X509) *chain);
+__owur int SSL_check_chain(SSL *s, X509 *x, EVP_PKEY *pk, STACK_OF(X509) *chain);
 
 #  define SSL_set_tlsext_host_name(s,name) \
 SSL_ctrl(s,SSL_CTRL_SET_TLSEXT_HOSTNAME,TLSEXT_NAMETYPE_host_name,(char *)name)