Fix target_os for mipsel-sony-psx

Previously set to `target_os = "none"` and `target_env = "psx"`, but
although the Playstation 1 is _close_ to a bare metal target in some
regards, it's still very much an operating system, so we should set
`target_os = "psx"`.

This also matches the `mipsel-sony-psp` target, which sets
`target_os = "psp"`.

compiler/rustc_target/src/spec/targets/mipsel_sony_psx.rs

@@ -14,8 +14,7 @@ pub(crate) fn target() -> Target {
         arch: "mips".into(),
 
         options: TargetOptions {
-            os: "none".into(),
-            env: "psx".into(),
+            os: "psx".into(),
             vendor: "sony".into(),
             linker_flavor: LinkerFlavor::Gnu(Cc::No, Lld::Yes),
             cpu: "mips1".into(),