Fix compiling issue on 32-bit environments.

Fix compiling issue on 32-bit environments.

It is reported that compiling src/parser/snprintf.c on 32-bit
environments fails due to undefined functions (isnan() and
ininf()). They come from math.h so include it.  snprintf.c was
imported from PostgreSQL long time ago. If we look into the original
file (src/port/snprintf.c) it actually has "#include <math.h>"
already. Including math.h was provided as a pull request:
https://github.com/pgpool/pgpool2/pull/128

I also added a minor modification to the patch to reorder the
positions of include files.

Author: Gyorgy Sarvari <skandigraun@gmail.com>
Discussion: https://www.postgresql.org/message-id/20250917.194736.353755422175293639.ishii%40postgresql.org
Backpatch-through: v4.2