Support pg_attribute_aligned and noreturn in MSVC

Over in the "Add last commit LSN to pg_last_committed_xact()" [1]
thread this patch had been added as a precursor, but Michael Paquier
suggested it be broken out separately, so I'm doing that here.

It turns out that MSVC supports both noreturn [2] [3] and alignment
[4] [5] attributes, so this patch adds support for those. MSVC also
supports a form of packing, but the implementation as I can tell
requires wrapping the entire struct (with a push/pop declaration set)
[6], which doesn't seem to match the style of macros we're using for
packing in other compilers, so I opted not to implement that
attribute.

James Coleman

1: https://www.postgresql.org/message-id/Yk6UgCGlZKuxRr4n%40paquier.xyz
2: 2008+ https://learn.microsoft.com/en-us/previous-versions/visualstudio/visual-studio-2008/k6ktzx3s(v=vs.90)
3. 2015+ https://learn.microsoft.com/en-us/cpp/c-language/noreturn?view=msvc-140
4. 2008+ https://learn.microsoft.com/en-us/previous-versions/visualstudio/visual-studio-2008/dabb5z75(v=vs.90)
5. 2015+ https://learn.microsoft.com/en-us/cpp/cpp/align-cpp?view=msvc-170
6. https://learn.microsoft.com/en-us/cpp/preprocessor/pack?view=msvc-170