windows: Adjust FD_SETSIZE via commandline define

When using precompiled headers, we cannot pre-define macros for the system
headers from within .c files, as headers are already processed before
the #define in the C file is reached. But we can pre-define using
-DFD_SETSIZE, as long as that's also used when building the precompiled header.

A few files #define FD_SETSIZE 1024 on windows, as the default is only 64. I
am hesitant to change FD_SETSIZE globally on windows, due to
src/backend/port/win32/socket.c using it to size on-stack arrays. Instead add
-DFD_SETSIZE=1024 when building the specific targets needing it.

We likely should move away from using select() in those places, but that's a
larger change.

Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Reviewed-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Reviewed-by: Justin Pryzby <pryzby@telsasoft.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/20221005190829.lda7ttalh4mzrvf4@awork3.anarazel.de
Discussion: https://postgr.es/m/CA+hUKG+50eOUbN++ocDc0Qnp9Pvmou23DSXu=ZA6fepOcftKqA@mail.gmail.com
Discussion: https://postgr.es/m/20190826054000.GE7005%40paquier.xyz

src/fe_utils/Makefile

@@ -34,6 +34,10 @@ OBJS = \
 	simple_list.o \
 	string_utils.o
 
+ifeq ($(PORTNAME), win32)
+override CPPFLAGS += -DFD_SETSIZE=1024
+endif
+
 all: libpgfeutils.a
 
 libpgfeutils.a: $(OBJS)

src/fe_utils/meson.build

@@ -24,6 +24,7 @@ fe_utils_sources += psqlscan
 fe_utils = static_library('libpgfeutils',
   fe_utils_sources + generated_headers,
   include_directories: [postgres_inc, libpq_inc],
+  c_args: host_system == 'windows' ? ['-DFD_SETSIZE=1024'] : [],
   dependencies: frontend_common_code,
   kwargs: default_lib_args,
 )

src/fe_utils/parallel_slot.c

@@ -12,8 +12,8 @@
  *-------------------------------------------------------------------------
  */
 
-#ifdef WIN32
-#define FD_SETSIZE 1024			/* must set before winsock2.h is included */
+#if defined(WIN32) && FD_SETSIZE < 1024
+#error FD_SETSIZE needs to have been increased
 #endif
 
 #include "postgres_fe.h"