Implement env parsing on Windows

Fixes #12056
Also, enables existing parsing logic for all Unix derived OSs

Signed-off-by: Jason T. Greene <jason.greene@redhat.com>

pkg/env/env_unix.go

@@ -1,4 +1,4 @@
-// +build linux darwin
+// +build !windows
 
 package env
 

pkg/env/env_unsupported.go

@@ -1,8 +0,0 @@
-// +build !linux,!darwin
-
-package env
-
-func ParseSlice(s []string) (map[string]string, error) {
-	m := make(map[string]string)
-	return m, nil
-}

pkg/env/env_windows.go

@@ -0,0 +1,25 @@
+package env
+
+// ParseSlice parses the specified slice and transforms it into an environment
+// map.
+func ParseSlice(s []string) (map[string]string, error) {
+	env := make(map[string]string, len(s))
+	for _, e := range s {
+		if len(e) > 0 && e[0] == '=' {
+			// The legacy Windows CMD command interpreter uses a hack, where to emulate
+			// DOS semantics, it uses an illegal (by windows definition) env name for
+			// state storage to avoid conlficting with user defined env names. This is
+			// used to preserve drive letter paths. E.g., typing c: from another drive
+			// will remember the last CWD because CMD stores it in an env named "=C:".
+			// Since these are illegal, they are filtered from standard user access but
+			// are still available in the underlying win32 API calls. Since they have
+			// zero value to a container, we filter as well.
+			continue
+		}
+
+		if err := parseEnv(env, e); err != nil {
+			return nil, err
+		}
+	}
+	return env, nil
+}