pgsql: Use ShmemInitStruct to allocate lwlock.c's shared memory

Use ShmemInitStruct to allocate lwlock.c's shared memory

It's nice to have them show up in pg_shmem_allocations like all other
shmem areas. ShmemInitStruct() depends on ShmemIndexLock, but only
after postmaster startup.

Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Discussion: https://www.postgresql.org/message-id/47aaf57e-1b7b-4e12-bda2-0316081ff50e@iki.fi

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/30d432502bf42343ec0f9ad599625cde0cb38e57

Modified Files
--------------
src/backend/postmaster/launch_backend.c |  6 ------
src/backend/storage/ipc/ipci.c          |  4 ++--
src/backend/storage/lmgr/lwlock.c       | 32 ++++++++++++++++++++++----------
src/include/storage/lwlock.h            |  7 +------
4 files changed, 25 insertions(+), 24 deletions(-)