Still need to #define inline for MSVC

I only tested with VS2015 earlier, but previous versions apparently still
don't know that standard C99 keyword though it's documented on MSDN...
diff --git a/include/mbedtls/md.h b/include/mbedtls/md.h
index 9465a5a..2a6cc0c 100644
--- a/include/mbedtls/md.h
+++ b/include/mbedtls/md.h
@@ -28,9 +28,9 @@
 
 #include <stddef.h>
 
-#if defined(__ARMCC_VERSION) && !defined(inline)
+#if ( defined(__ARMCC_VERSION) || defined(_MSC_VER) ) && !defined(inline)
 #define inline __inline
-#endif /* __ARMCC_VERSION */
+#endif
 
 #define MBEDTLS_ERR_MD_FEATURE_UNAVAILABLE                -0x5080  /**< The selected feature is not available. */
 #define MBEDTLS_ERR_MD_BAD_INPUT_DATA                     -0x5100  /**< Bad input parameters to function. */