Remove --disable-spinlocks.

A later change will require atomic support, so it wouldn't make sense
for a hypothetical new system not to be able to implement spinlocks.

Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us> (concept, not the patch)
Reviewed-by: Andres Freund <andres@anarazel.de> (concept, not the patch)
Discussion: https://postgr.es/m/3351991.1697728588%40sss.pgh.pa.us

src/backend/storage/ipc/ipci.c

@@ -94,7 +94,6 @@ CalculateShmemSize(int *num_semaphores)
 
 	/* Compute number of semaphores we'll need */
 	numSemas = ProcGlobalSemas();
-	numSemas += SpinlockSemas();
 
 	/* Return the number of semaphores if requested by the caller */
 	if (num_semaphores)
@@ -111,7 +110,6 @@ CalculateShmemSize(int *num_semaphores)
 	 */
 	size = 100000;
 	size = add_size(size, PGSemaphoreShmemSize(numSemas));
-	size = add_size(size, SpinlockSemaSize());
 	size = add_size(size, hash_estimate_size(SHMEM_INDEX_SIZE,
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
@@ -225,14 +223,6 @@ CreateSharedMemoryAndSemaphores(void)
 	 */
 	PGReserveSemaphores(numSemas);
 
-	/*
-	 * If spinlocks are disabled, initialize emulation layer (which depends on
-	 * semaphores, so the order is important here).
-	 */
-#ifndef HAVE_SPINLOCKS
-	SpinlockSemaInit();
-#endif
-
 	/*
 	 * Set up shared memory allocation mechanism
 	 */