windows: add support for syscall.runtimeSetenv

I missed this in https://github.com/tinygo-org/tinygo/pull/3391 (because
I didn't test on Windows, my fault).

src/runtime/env.go

@@ -0,0 +1,51 @@
+//go:build linux || darwin || windows
+
+package runtime
+
+// Update the C environment if cgo is loaded.
+// Called from Go 1.20 and above.
+//
+//go:linkname syscallSetenv syscall.runtimeSetenv
+func syscallSetenv(key, value string) {
+	keydata := cstring(key)
+	valdata := cstring(value)
+	setenv(&keydata[0], &valdata[0])
+	if key == "GODEBUG" && godebugUpdate != nil {
+		// Starting with Go 1.20, we need to call a callback (set by
+		// internal/godebug) to notify the GODEBUG environment variable has
+		// changed. This is necessary to get archive/zip to pass tests.
+		godebugUpdate(key, value)
+	}
+}
+
+// Update the C environment if cgo is loaded.
+// Called from Go 1.20 and above.
+//
+//go:linkname syscallUnsetenv syscall.runtimeUnsetenv
+func syscallUnsetenv(key string) {
+	keydata := cstring(key)
+	unsetenv(&keydata[0])
+}
+
+// Compatibility with Go 1.19 and below.
+//
+//go:linkname syscall_setenv_c syscall.setenv_c
+func syscall_setenv_c(key string, val string) {
+	syscallSetenv(key, val)
+}
+
+// Compatibility with Go 1.19 and below.
+//
+//go:linkname syscall_unsetenv_c syscall.unsetenv_c
+func syscall_unsetenv_c(key string) {
+	syscallUnsetenv(key)
+}
+
+// cstring converts a Go string to a C string.
+// borrowed from syscall
+func cstring(s string) []byte {
+	data := make([]byte, len(s)+1)
+	copy(data, s)
+	// final byte should be zero from the initial allocation
+	return data
+}

src/runtime/env_unix.go

@@ -2,56 +2,6 @@
 
 package runtime
 
-// Update the C environment if cgo is loaded.
-// Called from Go 1.20 and above.
-//
-//go:linkname syscallSetenv syscall.runtimeSetenv
-func syscallSetenv(key, value string) {
-	keydata := cstring(key)
-	valdata := cstring(value)
-	// ignore any errors
-	libc_setenv(&keydata[0], &valdata[0], 1)
-	if key == "GODEBUG" && godebugUpdate != nil {
-		// Starting with Go 1.20, we need to call a callback (set by
-		// internal/godebug) to notify the GODEBUG environment variable has
-		// changed. This is necessary to get archive/zip to pass tests.
-		godebugUpdate(key, value)
-	}
-}
-
-// Update the C environment if cgo is loaded.
-// Called from Go 1.20 and above.
-//
-//go:linkname syscallUnsetenv syscall.runtimeUnsetenv
-func syscallUnsetenv(key string) {
-	keydata := cstring(key)
-	// ignore any errors
-	libc_unsetenv(&keydata[0])
-}
-
-// Compatibility with Go 1.19 and below.
-//
-//go:linkname syscall_setenv_c syscall.setenv_c
-func syscall_setenv_c(key string, val string) {
-	syscallSetenv(key, val)
-}
-
-// Compatibility with Go 1.19 and below.
-//
-//go:linkname syscall_unsetenv_c syscall.unsetenv_c
-func syscall_unsetenv_c(key string) {
-	syscallUnsetenv(key)
-}
-
-// cstring converts a Go string to a C string.
-// borrowed from syscall
-func cstring(s string) []byte {
-	data := make([]byte, len(s)+1)
-	copy(data, s)
-	// final byte should be zero from the initial allocation
-	return data
-}
-
 // int setenv(const char *name, const char *val, int replace);
 //
 //export setenv
@@ -61,3 +11,13 @@ func libc_setenv(name *byte, val *byte, replace int32) int32
 //
 //export unsetenv
 func libc_unsetenv(name *byte) int32
+
+func setenv(key, val *byte) {
+	// ignore any errors
+	libc_setenv(key, val, 1)
+}
+
+func unsetenv(key *byte) {
+	// ignore any errors
+	libc_unsetenv(key)
+}

src/runtime/env_windows.go

@@ -0,0 +1,23 @@
+//go:build windows
+
+package runtime
+
+// Set environment variable in Windows:
+//
+//	BOOL SetEnvironmentVariableA(
+//	    [in]           LPCSTR lpName,
+//	    [in, optional] LPCSTR lpValue
+//	);
+//
+//export SetEnvironmentVariableA
+func _SetEnvironmentVariableA(key, val *byte) bool
+
+func setenv(key, val *byte) {
+	// ignore any errors
+	_SetEnvironmentVariableA(key, val)
+}
+
+func unsetenv(key *byte) {
+	// ignore any errors
+	_SetEnvironmentVariableA(key, nil)
+}