pgsql: Remove uses of register due to incompatibility with C++17 and up

Remove uses of register due to incompatibility with C++17 and up

The use in regexec.c could remain, since we only try to keep headers C++
clean. But there really doesn't seem to be a good reason to use register in
that spot.

Discussion: /messages/by-id/20220308185902.ibdqmasoaunzjrfc@alap3.anarazel.de

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/03bf971d2dc701d473705fd00891028d140dd5ae

Modified Files
--------------
.cirrus.yml | 4 +---
src/backend/regex/regexec.c | 2 +-
src/include/port/atomics/arch-x86.h | 2 +-
src/include/storage/s_lock.h | 14 +++++++-------
4 files changed, 10 insertions(+), 12 deletions(-)