Remove unused #include's from backend .c files

as determined by include-what-you-use (IWYU)

While IWYU also suggests to *add* a bunch of #include's (which is its
main purpose), this patch does not do that.  In some cases, a more
specific #include replaces another less specific one.

Some manual adjustments of the automatic result:

- IWYU currently doesn't know about includes that provide global
  variable declarations (like -Wmissing-variable-declarations), so
  those includes are being kept manually.

- All includes for port(ability) headers are being kept for now, to
  play it safe.

- No changes of catalog/pg_foo.h to catalog/pg_foo_d.h, to keep the
  patch from exploding in size.

Note that this patch touches just *.c files, so nothing declared in
header files changes in hidden ways.

As a small example, in src/backend/access/transam/rmgr.c, some IWYU
pragma annotations are added to handle a special case there.

Discussion: https://www.postgresql.org/message-id/flat/af837490-6b2f-46df-ba05-37ea6a6653fc%40eisentraut.org

src/backend/utils/misc/guc.c

@@ -25,6 +25,7 @@
 #include "postgres.h"
 
 #include <limits.h>
+#include <math.h>
 #include <sys/stat.h>
 #include <unistd.h>
 
@@ -35,6 +36,8 @@
 #include "catalog/pg_parameter_acl.h"
 #include "guc_internal.h"
 #include "libpq/pqformat.h"
+#include "libpq/protocol.h"
+#include "miscadmin.h"
 #include "parser/scansup.h"
 #include "port/pg_bitutils.h"
 #include "storage/fd.h"
@@ -42,10 +45,8 @@
 #include "storage/shmem.h"
 #include "tcop/tcopprot.h"
 #include "utils/acl.h"
-#include "utils/backend_status.h"
 #include "utils/builtins.h"
 #include "utils/conffiles.h"
-#include "utils/float.h"
 #include "utils/guc_tables.h"
 #include "utils/memutils.h"
 #include "utils/timestamp.h"

src/backend/utils/misc/guc_funcs.c

@@ -24,9 +24,9 @@
 #include "catalog/pg_parameter_acl.h"
 #include "funcapi.h"
 #include "guc_internal.h"
+#include "miscadmin.h"
 #include "parser/parse_type.h"
 #include "utils/acl.h"
-#include "utils/backend_status.h"
 #include "utils/builtins.h"
 #include "utils/guc_tables.h"
 #include "utils/snapmgr.h"

src/backend/utils/misc/guc_tables.c

@@ -84,7 +84,7 @@
 #include "utils/guc_tables.h"
 #include "utils/memutils.h"
 #include "utils/pg_locale.h"
-#include "utils/portal.h"
+#include "utils/plancache.h"
 #include "utils/ps_status.h"
 #include "utils/inval.h"
 #include "utils/xml.h"

src/backend/utils/misc/pg_config.c

@@ -14,7 +14,6 @@
 
 #include "postgres.h"
 
-#include "catalog/pg_type.h"
 #include "common/config_info.h"
 #include "funcapi.h"
 #include "miscadmin.h"

src/backend/utils/misc/pg_controldata.c

@@ -20,7 +20,6 @@
 #include "access/xlog.h"
 #include "access/xlog_internal.h"
 #include "catalog/pg_control.h"
-#include "catalog/pg_type.h"
 #include "common/controldata_utils.h"
 #include "funcapi.h"
 #include "miscadmin.h"

src/backend/utils/misc/ps_status.c

@@ -19,9 +19,7 @@
 #include <crt_externs.h>
 #endif
 
-#include "libpq/libpq.h"
 #include "miscadmin.h"
-#include "pgstat.h"
 #include "utils/guc.h"
 #include "utils/ps_status.h"
 

src/backend/utils/misc/rls.c

@@ -21,7 +21,7 @@
 #include "catalog/pg_class.h"
 #include "miscadmin.h"
 #include "utils/acl.h"
-#include "utils/builtins.h"
+#include "utils/fmgrprotos.h"
 #include "utils/lsyscache.h"
 #include "utils/rls.h"
 #include "utils/syscache.h"

src/backend/utils/misc/timeout.c

@@ -17,7 +17,7 @@
 #include <sys/time.h>
 
 #include "miscadmin.h"
-#include "storage/proc.h"
+#include "storage/latch.h"
 #include "utils/timeout.h"
 #include "utils/timestamp.h"