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/compat-1.2.h b/include/polarssl/compat-1.2.h
index d694015..37df541 100644
--- a/include/polarssl/compat-1.2.h
+++ b/include/polarssl/compat-1.2.h
@@ -41,13 +41,10 @@
 // Comment out to disable prototype change warnings
 #define SHOW_PROTOTYPE_CHANGE_WARNINGS
 
-#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
 
 #if defined(_MSC_VER)
 // MSVC does not support #warning