fix cross compiling for windows with mingw

apply_linux_patches.sh

@@ -0,0 +1,4 @@
+#!/bin/bash
+cd openvr
+git reset --hard
+git apply ../patches/mingw_build.path

build.rs

@@ -4,6 +4,18 @@ use std::env;
 use std::path::PathBuf;
 
 fn main() {
+    #[cfg(unix)]
+    {
+        use std::{fs, process::Command};
+        Command::new("bash")
+            .current_dir(fs::canonicalize(".").unwrap())
+            .arg("apply_linux_patches.sh")
+            .spawn()
+            .unwrap()
+            .wait()
+            .unwrap();
+    }
+
     let out_dir = PathBuf::from(env::var("OUT_DIR").expect("Missing OUT_DIR env var"));
 
     println!("cargo:rerun-if-changed=wrapper.hpp");
@@ -24,13 +36,17 @@ fn main() {
         .define("CMAKE_ARCHIVE_OUTPUT_DIRECTORY_RELEASE", &out_dir_str)
         .define("CMAKE_RUNTIME_OUTPUT_DIRECTORY_DEBUG", &out_dir_str)
         .define("CMAKE_RUNTIME_OUTPUT_DIRECTORY_RELEASE", &out_dir_str)
-        .out_dir(&out_dir); 
+        .out_dir(&out_dir);
 
     if target_os == "macos" {
         config.define("BUILD_UNIVERSAL", "OFF");
     } else if target_os == "windows" {
         // Work around broken cmake build.
-        config.cxxflag("/DWIN32");
+        if env::var("CARGO_CFG_TARGET_ENV").unwrap() == "gnu" {
+            config.cxxflag("-DWIN32");
+        } else {
+            config.cxxflag("/DWIN32");
+        }
     }
 
     let dst = config.build();
@@ -61,4 +77,16 @@ fn main() {
         .expect("could not generate bindings")
         .write_to_file(out_dir.join("bindings.rs"))
         .expect("could not write bindings.rs");
+    #[cfg(unix)]
+    {
+        use std::{fs, process::Command};
+        //reset openvr submodule so git doesn't say it's dirty
+        Command::new("bash")
+            .current_dir(fs::canonicalize(".").unwrap())
+            .arg("reset_openvr_submodule.sh")
+            .spawn()
+            .unwrap()
+            .wait()
+            .unwrap();
+    }
 }

patches/mingw_build.path

@@ -0,0 +1,13 @@
+diff --git a/headers/openvr_capi.h b/headers/openvr_capi.h
+index c4b6877..0d6fdbf 100644
+--- a/headers/openvr_capi.h
++++ b/headers/openvr_capi.h
+@@ -48,7 +48,7 @@
+
+ #include <stdint.h>
+
+-#if defined( __WIN32 )
++#if defined( __WIN32 ) && !defined(__MINGW32__)
+ typedef char bool;
+ #else
+ #include <stdbool.h>

reset_openvr_submodule.sh

@@ -0,0 +1,3 @@
+#!/bin/bash
+cd openvr
+git reset --hard