pgsql: With ancient gcc, skip pg_attribute_printf() on function pointer

With ancient gcc, skip pg_attribute_printf() on function pointer.

Buildfarm results show that the ability to attach pg_attribute_printf
decoration to a function pointer appeared somewhere between gcc 2.95.3
and gcc 4.0.1.  Guess that it was there in 4.0.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/b46d9beb658af7eb4e2a08dfa34206a117c9654f

Modified Files
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src/bin/psql/psqlscan.h | 5 +++++
1 file changed, 5 insertions(+)