pgsql: Fix omissions in snprintf.c's coverage of standard *printf funct

Fix omissions in snprintf.c's coverage of standard *printf functions.

A warning on a NetBSD box revealed to me that pg_waldump/compat.c
is using vprintf(), which snprintf.c did not provide coverage for.
This is not good if we want to have uniform *printf behavior, and
it's pretty silly to omit when it's a one-line function.

I also noted that snprintf.c has pg_vsprintf() but for some reason
it was not exposed to the outside world, creating another way in
which code might accidentally invoke the platform *printf family.

Let's just make sure that we replace all eight of the POSIX-standard
printf family.

Also, upgrade plperl.h and plpython.h to make sure that they do
their undefine/redefine rain dance for all eight, not some random
maybe-sufficient subset thereof.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7767aadd94cd252a12fa00f6122ad4dd10455791

Modified Files
--------------
src/include/port.h | 10 ++++++++++
src/pl/plperl/plperl.h | 40 +++++++++++++++++++++++++++++++++++-----
src/pl/plpython/plpython.h | 43 +++++++++++++++++++++++++++++++++++++------
src/port/snprintf.c | 10 +++++++++-
4 files changed, 91 insertions(+), 12 deletions(-)