Fix macroization of inline in C++

When compiling as C++, MSVC complains about our macroization of a keyword.
Stop doing that as we know inline is always available in C++
diff --git a/include/polarssl/ssl.h b/include/polarssl/ssl.h
index 1f9f8be..3b67d38 100644
--- a/include/polarssl/ssl.h
+++ b/include/polarssl/ssl.h
@@ -97,13 +97,10 @@
 #define POLARSSL_KEY_EXCHANGE__SOME__ECDHE_ENABLED
 #endif
 
-#if defined(_MSC_VER) && !defined(inline)
-#define inline _inline
-#else
-#if defined(__ARMCC_VERSION) && !defined(inline)
+#if ( defined(__ARMCC_VERSION) || defined(_MSC_VER) ) && \
+    !defined(inline) && !defined(__cplusplus)
 #define inline __inline
-#endif /* __ARMCC_VERSION */
-#endif /*_MSC_VER */
+#endif
 
 /*
  * SSL Error codes