Tidy up alignof #defines.

We haven't supported MSVC 2013 for a while (we may even be able to drop
2015 in not too long). There is also no need to pull in stdalign.h in
C++. alignof and alignas are keywords.

Change-Id: Ib31d8166282592bcb9e1c543e57758ff55746404
Reviewed-on: https://boringssl-review.googlesource.com/20704
Commit-Queue: Steven Valdez <svaldez@google.com>
Reviewed-by: Steven Valdez <svaldez@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/crypto/internal.h b/crypto/internal.h
index 87b69da..76d39b7 100644
--- a/crypto/internal.h
+++ b/crypto/internal.h
@@ -116,14 +116,14 @@
 #include <assert.h>
 #include <string.h>
 
+#if !defined(__cplusplus)
 #if defined(_MSC_VER)
-#if !defined(__cplusplus) || _MSC_VER < 1900
 #define alignas(x) __declspec(align(x))
 #define alignof __alignof
-#endif
 #else
 #include <stdalign.h>
 #endif
+#endif
 
 #if !defined(OPENSSL_NO_THREADS) && \
     (!defined(OPENSSL_WINDOWS) || defined(__MINGW32__))