Building with c++14/17 fails on clang

[danlark1]

Describe the bug

When building with C++17, zstd fails

[./third_party/zstdlib/zstd.h:191]:1: error: an attribute list cannot appear here
ZSTD_DEPRECATED("Replaced by ZSTD_getFrameContentSize")
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[./third_party/zstdlib/zstd.h:49]:38: note: expanded from macro 'ZSTD_DEPRECATED'
#    define ZSTD_DEPRECATED(message) [[deprecated(message)]]
                                     ^~~~~~~~~~~~~~~~~~~~~~~

I believe it came from

https://github.com/facebook/zstd/pull/3225/files

where before it was

if defined (__cplusplus) && (__cplusplus >= 201402) /* C++14 or greater */
#    define ZSTD_DEPRECATED(message) [[deprecated(message)]] ZSTDLIB_STATIC_API

And after it became in reverse order

ZSTDLIB_API
ZSTD_DEPRECATED("Replaced by ZSTD_getFrameContentSize")
unsigned long long ZSTD_getDecompressedSize(const void* src, size_t srcSize);

I see that the order is slightly inconsistent throughout the file, for example in c450f9f the order of ZSTD_DEPRECATED/ZSTDLIB_API in reversed

To Reproduce

1. Include ZSTD in a C++ source file and build with C++14/17

Expected behavior
Builds

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Desktop (please complete the following information):

• OS: Linux
• Version 1.5.3
• Compiler clang
• Flags -std=c++17
• Other relevant hardware specs [e.g. Dual-core]
• Build system CMake, Makefile