pgsql: Make our back branches build under -fkeep-inline-functions.

Make our back branches build under -fkeep-inline-functions.

Add "#ifndef FRONTEND" where necessary to make pg_waldump build
on compilers that don't elide unused static-inline functions.

This back-patches relevant parts of commit 3e9ca5260, fixing build
breakage from dc7420c2c and back-patching of f10f0ae42.

Per recently-resurrected buildfarm member castoroides.  We aren't
expecting castoroides to build anything newer than v11, but we
might as well clean up the intermediate branches while at it.

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/21c058648ec2cd257b7b8bb10b98e08564a685a4

Modified Files
--------------
src/include/utils/rel.h     | 2 ++
src/include/utils/snapmgr.h | 2 ++
2 files changed, 4 insertions(+)