We don't need to include pg_sema.h in s_lock.h anymore.

Minor improvement to commit daa7527afc:
s_lock.h no longer has any need to mention PGSemaphoreData, so we can
rip out the #include that supplies that.  In a non-HAVE_SPINLOCKS
build, this doesn't really buy much since we still need the #include
in spin.h --- but everywhere else, this reduces #include footprint by
some trifle, and helps keep the different locking facilities separate.

src/backend/storage/lmgr/spin.c

@@ -26,6 +26,7 @@
 #include "miscadmin.h"
 #include "replication/walsender.h"
 #include "storage/lwlock.h"
+#include "storage/pg_sema.h"
 #include "storage/spin.h"
 
 

src/include/storage/s_lock.h

@@ -94,11 +94,8 @@
 #ifndef S_LOCK_H
 #define S_LOCK_H
 
-#include "storage/pg_sema.h"
-
 #ifdef HAVE_SPINLOCKS	/* skip spinlocks if requested */
 
-
 #if defined(__GNUC__) || defined(__INTEL_COMPILER)
 /*************************************************************************
  * All the gcc inlines

src/include/storage/spin.h

@@ -57,6 +57,9 @@
 #define SPIN_H
 
 #include "storage/s_lock.h"
+#ifndef HAVE_SPINLOCKS
+#include "storage/pg_sema.h"
+#endif
 
 
 #define SpinLockInit(lock)	S_INIT_LOCK(lock)