Fix path env on cygwin when cross compiling from Windows

Cargo.lock

@@ -117,6 +117,7 @@ dependencies = [
  "rust-embed",
  "serial_test",
  "terminfo",
+ "unix_path",
  "widestring",
 ]
 
@@ -545,6 +546,21 @@ version = "1.0.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "adb9e6ca4f869e1180728b7950e35922a7fc6397f7b641499e8f3ef06e50dc83"
 
+[[package]]
+name = "unix_path"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "af8e291873ae77c4c8d9c9b34d0bee68a35b048fb39c263a5155e0e353783eaf"
+dependencies = [
+ "unix_str",
+]
+
+[[package]]
+name = "unix_str"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2ace0b4755d0a2959962769239d56267f8a024fef2d9b32666b3dcd0946b0906"
+
 [[package]]
 name = "version_check"
 version = "0.9.5"

Cargo.toml

@@ -71,6 +71,9 @@ serial_test = { version = "3", default-features = false }
 cc = "1.0.94"
 rsconf = "0.2.2"
 
+[target.'cfg(windows)'.build-dependencies]
+unix_path = "1.0.1"
+
 [lib]
 crate-type = ["rlib"]
 path = "src/lib.rs"

build.rs

@@ -3,7 +3,7 @@
 use rsconf::{LinkType, Target};
 use std::env;
 use std::error::Error;
-use std::path::{Path, PathBuf};
+use std::path::Path;
 
 fn main() {
     setup_paths();
@@ -232,6 +232,11 @@ fn has_small_stack(_: &Target) -> Result<bool, Box<dyn Error>> {
 }
 
 fn setup_paths() {
+    #[cfg(unix)]
+    use std::path::PathBuf;
+    #[cfg(windows)]
+    use unix_path::{Path, PathBuf};
+
     fn get_path(name: &str, default: &str, onvar: &Path) -> PathBuf {
         let mut var = PathBuf::from(env::var(name).unwrap_or(default.to_string()));
         if var.is_relative() {