build: add Windows support

README.md

@@ -100,6 +100,31 @@ system instead, without success. If someone more skilled at the
 build system than the previous author strolls along, please 
 take a look.
 
+### Cross-compiling from Linux to Windows
+
+Building binaries for Windows must happen through cross-compiling 
+from a Linux machine. This requires a rather specific set of 
+packages on the host machine, so the easiest way is to do this
+through a Docker container. We use the `electriccoinco/zcashd-build-ubuntu-jammy`
+image, provided by the upstream Zcash devs.
+
+```bash
+# from the root of this repo
+$ docker run -ti -v $PWD:/zside --workdir /zside electriccoinco/zcashd-build-ubuntu-jammy bash
+
+$ HOST=x86_64-w64-mingw32 make -C depends V=1 -j8
+$ export CONFIG_SITE=$PWD/depends/x86_64-w64-mingw32/share/config.site
+$ ./autogen.sh
+$ ./configure --disable-tests --disable-bench --disable-hardening --enable-online-rust
+$ make -C src cargo-build-lib
+$ BRIDGE_LOCATION=$(dirname $(./contrib/devtools/find-libcxxbridge.sh))
+$ export LDFLAGS="-L$BRIDGE_LOCATION -lcxxbridge1" 
+$ ./configure --disable-tests --disable-bench --disable-hardening --enable-online-rust
+$ make -j8
+
+# final result is in ./src/zsided.exe
+```
+
 ### Nix - currently not working
 
 To install all dependencies and build zcash-sidechain on ubuntu (22.04) run:

configure.ac

@@ -405,6 +405,9 @@ case $host in
 
      CPPFLAGS="$CPPFLAGS -D_MT -DWIN32 -D_WINDOWS -DBOOST_THREAD_USE_LIB -D_WIN32_WINNT=0x0601 -D_WIN32_IE=0x0501 -DWIN32_LEAN_AND_MEAN"
      LEVELDB_TARGET_FLAGS="-DOS_WINDOWS"
+
+     dnl Windows seems to require libssp even if hardening is disabled.
+     LDFLAGS="$LDFLAGS -lssp"
 
      dnl libtool insists upon adding -nostdlib and a list of objects/libs to link against.
      dnl That breaks our ability to build dll's with static libgcc/libstdc++/libssp. Override