MSVC's macro VA_ARGS support behaves slightly differently from
gcc/clang, where VA_ARGS is treated as a single token when passed to
other macros, e.g.

    #define FIRST(X, ...) 'X'
    #define FOO(...) FIRST(__VA_ARGS__)
    FOO(a,b,c)

expands to

    gcc/clang: 'a'
    MSVC: 'a,b,c'

The workaround to this is to wrap the call in a no-op macro, which
expands VA_ARGS first, and only then passes it through:

    #define EXPAND(x) x
    #define FOO(...) EXPAND(FIRST(__VA_ARGS__))

This was causing errors on windows builds when CSA_ASSERT was passed
multiple additional expressions.

Change-Id: Ia40bf23baf97af29c7f6f67c8a83918ecca15364
Reviewed-on: https://chromium-review.googlesource.com/586831Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46927}