Rename identifiers containing double-underscore
Rename identifiers containing double-underscore (`__`) to avoid `__`.
The reason to avoid double-underscore is that all identifiers
containing double-underscore are reserved in C++. Rename all such
identifiers that appear in any public header, including ssl_internal.h
which is in principle private but in practice is installed with the
public headers.
This commit makes check-names.sh pass.
```
perl -i -pe 's/\bMBEDTLS_SSL__ECP_RESTARTABLE\b/MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED/g; s/\bMBEDTLS_KEY_EXCHANGE_(_\w+)_(_\w+)\b/MBEDTLS_KEY_EXCHANGE${1}${2}/g' include/mbedtls/*.h library/*.c programs/*/*.c scripts/data_files/rename-1.3-2.0.txt tests/suites/*.function
```
diff --git a/tests/suites/test_suite_ssl.function b/tests/suites/test_suite_ssl.function
index 44e2227..d32d9dd 100644
--- a/tests/suites/test_suite_ssl.function
+++ b/tests/suites/test_suite_ssl.function
@@ -1635,7 +1635,7 @@
int forced_ciphersuite[2];
enum { BUFFSIZE = 17000 };
mbedtls_endpoint client, server;
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
const char *psk_identity = "foo";
#endif
#if defined(MBEDTLS_TIMING_C)
@@ -1723,7 +1723,7 @@
TEST_ASSERT( MBEDTLS_SSL_MAX_FRAG_LEN_NONE == options->mfl );
#endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
if( options->psk_str != NULL && options->psk_str->len > 0 )
{
TEST_ASSERT( mbedtls_ssl_conf_psk( &client.conf, options->psk_str->x,