add windows cross-build tool chain

.github/workflows/build-release.yaml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       matrix:
         # build and publish in parallel: linux/386, linux/amd64, linux/arm64, windows/386, windows/amd64, darwin/amd64, darwin/arm64
-        goos: [ linux, windows ]
+        goos: [ windows ]
         goarch: [ amd64, arm64 ]
         exclude:
           - goarch: arm64

Makefile

@@ -107,9 +107,9 @@ generate: install-tools
 .PHONY: install-cross-build-tools
 install-cross-build-tools:
 	if [ "$(UNAME)" = "Debian" ] ; then \
-		apt-get update && apt-get -y install apt-utils gcc-aarch64-linux-gnu ; \
+		apt-get update && apt-get -y install apt-utils gcc-aarch64-linux-gnu gcc-mingw-w64-x86-64 ; \
 	elif [ "$(UNAME)" = "Linux" ] ; then \
-		apt-get update && apt-get -y install apt-utils gcc-aarch64-linux-gnu ; \
+		apt-get update && apt-get -y install apt-utils gcc-aarch64-linux-gnu gcc-mingw-w64-x86-64 ; \
 	else \
 		echo "this target only works on Debian or Linux, host runs on" $(UNAME) ; \
 	fi

pre_build.sh

@@ -3,17 +3,34 @@
 # Exit as soon as any command fails
 set -e
 
-# INPUT_GOARCH is a variable set by the wangyoucao577 action
+# INPUT_GOARCH and INPUT_GOOS are set by the wangyoucao577 action:
 # https://github.com/wangyoucao577/go-release-action/blob/v1.40/action.yml#L109
+# it represents the target arch and target os
+
+export GOOS=${INPUT_GOOS} 
+export GOARCH=${INPUT_GOARCH}
+
 C_COMP=""
-if [ "${INPUT_GOARCH}" = "arm64" ]; then
-    C_COMP="aarch64-linux-gnu-gcc"
-elif [ "${INPUT_GOARCH}" = "amd64" ]; then
-    C_COMP="x86_64-linux-gnu-gcc"
+if [ "${GOOS}" = "linux" ]; then
+    if [ "${GOARCH}" = "arm64" ]; then
+        C_COMP="aarch64-linux-gnu-gcc"
+    elif [ "${GOARCH}" = "amd64" ]; then
+        C_COMP="x86_64-linux-gnu-gcc"
+    fi
+elif [ "${GOOS}" = "windows" ]; then
+    if [ "${GOARCH}" = "amd64" ]; then
+        C_COMP="gcc-mingw-w64-x86-64"
+    else 
+        { echo "arm64 on windows isn't supported"; exit 1; }
+    fi
 fi
 
+
 export GO111MODULE=on
+# enable CGO because it is requiired by the onflow/crypto package
 export CGO_ENABLED=1
+# set the correct C compiler
 export CC=${C_COMP}
+# this flag disables non-portable code that requires specific CPU features.
 export CGO_FLAGS=\""-O2 -D__BLST_PORTABLE__"\"