Rollup merge of #45892 - redox-os:is_absolute_fix, r=alexcrichton

Redox: Return true from Path::is_absolute if a Path contains root or a scheme

In Redox, different subsystems have different filesystem paths. However, the majority of applications using the `Path::is_absolute` function really only want to know if a path is absolute from the perspective of the scheme it is currently running in, usually `file:`. This makes both `file:/` and `/` return `true` from `Path::is_absolute`, meaning that most code does not have to check if it is running on Redox.

Code that wants to know if a path contains a scheme can implement such a check on its own.

Related to #45893

Author: kennytm

src/libstd/path.rs

@@ -1690,11 +1690,11 @@ impl Path {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[allow(deprecated)]
     pub fn is_absolute(&self) -> bool {
-        if !cfg!(target_os = "redox") {
-            self.has_root() && (cfg!(unix) || self.prefix().is_some())
-        } else {
+        if cfg!(target_os = "redox") {
             // FIXME: Allow Redox prefixes
-            has_redox_scheme(self.as_u8_slice())
+            self.has_root() || has_redox_scheme(self.as_u8_slice())
+        } else {
+            self.has_root() && (cfg!(unix) || self.prefix().is_some())
         }
     }