Improved windows host support (git bash & cygwin)

When using windows as a host OS, GOROOT must be a Windows path.
This condition applies whenever invoking go, either as part of
the installation or when written into the .env file.  Also,
the .exe files in the Windows Go distribution do not have
an executable flag set.  This change addresses both of these
issues, allowing at least binary installs to run correctly when
running under git bash or cygwin.

gimme

@@ -355,11 +355,22 @@ EOF
 
 # _env "dir"
 _env() {
+	if [[ -d "${1}/bin" && -f "${1}/bin/go.exe" && "$GIMME_HOSTOS" == windows ]] && command -v cygpath &>/dev/null
+	then
+		# .exe's don't come in from the .zip with the executable flag set
+		chmod +x "${1}/bin/"*.exe
+		# $1 is a cygwin/msys path, but GOROOT needs a Windows path
+		local -x GOROOT
+		GOROOT="$(cygpath -wa "$1")"
+	else
+		local -x GOROOT="$1"
+	fi
+
 	[[ -d "${1}/bin" && -x "${1}/bin/go" ]] || return 1
 
 	# if we try to run a Darwin binary on Linux, we need to fail so 'auto' can fallback to cross-compiling from source
 	# automatically
-	GOROOT="${1}" "${1}/bin/go" version &>/dev/null || return 1
+	"${1}/bin/go" version &>/dev/null || return 1
 
 	# https://twitter.com/davecheney/status/431581286918934528
 	# we have to GOROOT sometimes because we use official release binaries in unofficial locations :(
@@ -370,18 +381,19 @@ _env() {
 	#   Tools like `gimme` are the reason that GOROOT-in-env exists.
 
 	echo
-	if [[ "$(GOROOT="${1}" "${1}/bin/go" env GOHOSTOS)" == "${GIMME_OS}" ]]; then
+	if [[ "$("${1}/bin/go" env GOHOSTOS)" == "${GIMME_OS}" ]]; then
 		echo 'unset GOOS;'
 	else
 		echo 'export GOOS="'"${GIMME_OS}"'";'
 	fi
-	if [[ "$(GOROOT="${1}" "${1}/bin/go" env GOHOSTARCH)" == "${GIMME_ARCH}" ]]; then
+	if [[ "$("${1}/bin/go" env GOHOSTARCH)" == "${GIMME_ARCH}" ]]; then
 		echo 'unset GOARCH;'
 	else
 		echo 'export GOARCH="'"${GIMME_ARCH}"'";'
 	fi
 
-	echo "export GOROOT='${1}';"
+	# GOROOT on Windows can contain \, so ensure it is shell-quoted
+	printf 'export GOROOT=%q;\n' "$GOROOT"
 
 	# shellcheck disable=SC2016
 	echo 'export PATH="'"${1}/bin"':${PATH}";'
@@ -393,12 +405,20 @@ _env() {
 
 # _env_alias "dir" "env-file"
 _env_alias() {
+	if [[ "$GIMME_HOSTOS" == windows ]] && command -v cygpath &>/dev/null; then
+		# $1 is a cygwin/msys path, but GOROOT needs a Windows path
+		local -x GOROOT
+		GOROOT="$(cygpath -wa "$1")"
+	else
+		local -x GOROOT="$1"
+	fi
+
 	if [[ "${GIMME_NO_ENV_ALIAS}" ]]; then
 		echo "${2}"
 		return
 	fi
 
-	if [[ "$(GOROOT="${1}" "${1}/bin/go" env GOHOSTOS)" == "${GIMME_OS}" && "$(GOROOT="${1}" "${1}/bin/go" env GOHOSTARCH)" == "${GIMME_ARCH}" ]]; then
+	if [[ "$("${1}/bin/go" env GOHOSTOS)" == "${GIMME_OS}" && "$("${1}/bin/go" env GOHOSTARCH)" == "${GIMME_ARCH}" ]]; then
 		# GIMME_GO_VERSION might be a branch, which can contain '/'
 		local dest="${GIMME_ENV_PREFIX}/go${GIMME_GO_VERSION//\//__}.env"
 		cp "${2}" "${dest}"
@@ -799,7 +819,7 @@ case "${GIMME_VERSION_PREFIX}" in
 	;;
 esac
 
-case "${GIMME_OS}" in mingw* | msys_nt*)
+case "${GIMME_OS}" in mingw* | msys_nt* | cygwin_nt-*)
 	# Minimalist GNU for Windows
 	GIMME_OS='windows'
 
@@ -811,6 +831,18 @@ case "${GIMME_OS}" in mingw* | msys_nt*)
 	;;
 esac
 
+case "${GIMME_HOSTOS}" in mingw* | msys_nt* | cygwin_nt-*)
+	# Minimalist GNU for Windows
+	GIMME_HOSTOS='windows'
+
+	if [ "${GIMME_HOSTARCH}" = 'i686' ]; then
+		GIMME_HOSTARCH="386"
+	else
+		GIMME_HOSTARCH="amd64"
+	fi
+	;;
+esac
+
 force_install=0
 force_known_update=0