pgsql: Work around buggy alignas in older g++

Work around buggy alignas in older g++

Older g++ (<9.3) mishandle the alignas specifier (raise warnings that
the alignment is too large), but the more or less equivalent attribute
works. So as a workaround, #define alignas to that attribute for
those versions.

see <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89357&gt;

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: /messages/by-id/3119480.1769189606@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/a9bdb63bba8a631cd4797393307eecf5fcde9167

Modified Files
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src/include/c.h | 10 ++++++++++
1 file changed, 10 insertions(+)