pgsql: Be more careful to avoid including system headers after perl.h

Be more careful to avoid including system headers after perl.h

Commit 121d2d3d70 included simd.h into pg_wchar.h. This caused a problem
on Windows, since Perl has "#define free" (referring to globals), which
breaks the Windows' header. To fix, move the static inline function
definitions from plperl_helpers.h, into plperl.h, where we already
document the necessary inclusion order. Since those functions were the
only reason for the existence of plperl_helpers.h, remove it.

First reported by Justin Pryzby

Diagnosis and review by Andres Freund, patch by myself per suggestion
from Tom Lane

Discussion: https://www.postgresql.org/message-id/20220826115546.GE2342%40telsasoft.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4eec2e03c34f9a357d86317b1cd05d80a2ab559d

Modified Files
--------------
contrib/hstore_plperl/hstore_plperl.c |   1 -
contrib/jsonb_plperl/jsonb_plperl.c   |   1 -
src/pl/plperl/GNUmakefile             |   4 +-
src/pl/plperl/SPI.xs                  |   1 -
src/pl/plperl/Util.xs                 |   1 -
src/pl/plperl/plperl.c                |   2 -
src/pl/plperl/plperl.h                | 170 ++++++++++++++++++++++++++++++++-
src/pl/plperl/plperl_helpers.h        | 171 ----------------------------------
8 files changed, 171 insertions(+), 180 deletions(-)