Second attempt to silence SSL compile failures on hamerkop.

After further investigation, it seems the cause of the problem
is our recent decision to start defining WIN32_LEAN_AND_MEAN.
That causes <windows.h> to no longer include <wincrypt.h>, which
means that the OpenSSL headers are unable to prevent conflicts
with that header by #undef'ing the conflicting macros.  Apparently,
some other system header that be-secure-openssl.c #includes after
the OpenSSL headers is pulling in <wincrypt.h>.  It's obscure just
where that happens and why we're not seeing it on other Windows
buildfarm animals.  However, it should work to move the OpenSSL
#includes to the end of the list.  For the sake of future-proofing,
do likewise in fe-secure-openssl.c.  In passing, remove useless
double inclusions of <openssl/ssl.h>.

Thanks to Thomas Munro for running down the relevant information.

Discussion: https://postgr.es/m/1051867.1635720347@sss.pgh.pa.us

src/backend/libpq/be-secure-openssl.c

@@ -29,15 +29,6 @@
 #include <arpa/inet.h>
 #endif
 
-#include <openssl/ssl.h>
-#include <openssl/conf.h>
-#include <openssl/dh.h>
-#ifndef OPENSSL_NO_ECDH
-#include <openssl/ec.h>
-#endif
-#include <openssl/x509v3.h>
-
-#include "common/openssl.h"
 #include "libpq/libpq.h"
 #include "miscadmin.h"
 #include "pgstat.h"
@@ -46,6 +37,21 @@
 #include "tcop/tcopprot.h"
 #include "utils/memutils.h"
 
+/*
+ * These SSL-related #includes must come after all system-provided headers.
+ * This ensures that OpenSSL can take care of conflicts with Windows'
+ * <wincrypt.h> by #undef'ing the conflicting macros.  (We don't directly
+ * include <wincrypt.h>, but some other Windows headers do.)
+ */
+#include "common/openssl.h"
+#include <openssl/conf.h>
+#include <openssl/dh.h>
+#ifndef OPENSSL_NO_ECDH
+#include <openssl/ec.h>
+#endif
+#include <openssl/x509v3.h>
+
+
 /* default init hook can be overridden by a shared library */
 static void default_openssl_tls_init(SSL_CTX *context, bool isServerStart);
 openssl_tls_init_hook_typ openssl_tls_init_hook = default_openssl_tls_init;

src/interfaces/libpq/fe-secure-openssl.c

@@ -30,7 +30,6 @@
 #include "fe-auth.h"
 #include "fe-secure-common.h"
 #include "libpq-int.h"
-#include "common/openssl.h"
 
 #ifdef WIN32
 #include "win32.h"
@@ -55,13 +54,20 @@
 #endif
 #endif
 
-#include <openssl/ssl.h>
+/*
+ * These SSL-related #includes must come after all system-provided headers.
+ * This ensures that OpenSSL can take care of conflicts with Windows'
+ * <wincrypt.h> by #undef'ing the conflicting macros.  (We don't directly
+ * include <wincrypt.h>, but some other Windows headers do.)
+ */
+#include "common/openssl.h"
 #include <openssl/conf.h>
 #ifdef USE_SSL_ENGINE
 #include <openssl/engine.h>
 #endif
 #include <openssl/x509v3.h>
 
+
 static int	verify_cb(int ok, X509_STORE_CTX *ctx);
 static int	openssl_verify_peer_name_matches_certificate_name(PGconn *conn,
 															  ASN1_STRING *name,