Use winpty to launch fzf in Git bash (mintty)

Close #3806

Known limitation:
* --height cannot be used

src/proxy_unix.go

@@ -0,0 +1,38 @@
+//go:build !windows
+
+package fzf
+
+import (
+	"io"
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+func sh() (string, error) {
+	return "sh", nil
+}
+
+func mkfifo(path string, mode uint32) (string, error) {
+	return path, unix.Mkfifo(path, mode)
+}
+
+func withOutputPipe(output string, task func(io.ReadCloser)) error {
+	outputFile, err := os.OpenFile(output, os.O_RDONLY, 0)
+	if err != nil {
+		return err
+	}
+	task(outputFile)
+	outputFile.Close()
+	return nil
+}
+
+func withInputPipe(input string, task func(io.WriteCloser)) error {
+	inputFile, err := os.OpenFile(input, os.O_WRONLY, 0)
+	if err != nil {
+		return err
+	}
+	task(inputFile)
+	inputFile.Close()
+	return nil
+}