merge bitcoin#19375: target Windows 7 when building libevent and fix ipv6 usage

depends/packages/libevent.mk

@@ -3,17 +3,23 @@ $(package)_version=2.1.11-stable
 $(package)_download_path=https://github.com/libevent/libevent/archive/
 $(package)_file_name=release-$($(package)_version).tar.gz
 $(package)_sha256_hash=229393ab2bf0dc94694f21836846b424f3532585bac3468738b7bf752c03901e
+$(package)_patches=0001-fix-windows-getaddrinfo.patch
 
 define $(package)_preprocess_cmds
+   patch -p1 < $($(package)_patch_dir)/0001-fix-windows-getaddrinfo.patch && \
   ./autogen.sh
 endef
 
+# When building for Windows, we set _WIN32_WINNT to target the same Windows
+# version as we do in configure. Due to quirks in libevents build system, this
+# is also required to enable support for ipv6. See #19375.
 define $(package)_set_vars
   $(package)_config_opts=--disable-shared --disable-openssl --disable-libevent-regress --disable-samples
   $(package)_config_opts += --disable-dependency-tracking --enable-option-checking
   $(package)_config_opts_release=--disable-debug-mode
   $(package)_config_opts_linux=--with-pic
   $(package)_config_opts_android=--with-pic
+  $(package)_cppflags_mingw32=-D_WIN32_WINNT=0x0601
 endef
 
 define $(package)_config_cmds

depends/patches/libevent/0001-fix-windows-getaddrinfo.patch

@@ -0,0 +1,15 @@
+diff -ur libevent-2.1.8-stable.orig/configure.ac libevent-2.1.8-stable/configure.ac
+--- libevent-2.1.8-stable.orig/configure.ac	2017-01-29 17:51:00.000000000 +0000
++++ libevent-2.1.8-stable/configure.ac	2020-03-07 01:11:16.311335005 +0000
+@@ -389,6 +389,10 @@
+ 		#ifdef HAVE_NETDB_H
+ 		#include <netdb.h>
+ 		#endif
++#ifdef _WIN32
++#include <winsock2.h>
++#include <ws2tcpip.h>
++#endif
+ 	    ]],
+ 	    [[
+ 		getaddrinfo;
+Only in libevent-2.1.8-stable: configure.ac~