rustc_target: introduce Os

Improve type safety by using an enum rather than strings.

Author: tamird

src/lib.rs

@@ -49,7 +49,7 @@ use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
 use rustc_session::Session;
 use rustc_session::config::OutputFilenames;
 use rustc_span::{Symbol, sym};
-use rustc_target::spec::{Abi, Arch, Env};
+use rustc_target::spec::{Abi, Arch, Env, Os};
 
 pub use crate::config::*;
 use crate::prelude::*;
@@ -163,15 +163,15 @@ impl CodegenBackend for CraneliftCodegenBackend {
     fn target_config(&self, sess: &Session) -> TargetConfig {
         // FIXME return the actually used target features. this is necessary for #[cfg(target_feature)]
         let target_features = match sess.target.arch {
-            Arch::X86_64 if sess.target.os != "none" => {
+            Arch::X86_64 if sess.target.os != Os::None => {
                 // x86_64 mandates SSE2 support and rustc requires the x87 feature to be enabled
                 vec![sym::fxsr, sym::sse, sym::sse2, Symbol::intern("x87")]
             }
-            Arch::AArch64 => match &*sess.target.os {
-                "none" => vec![],
+            Arch::AArch64 => match &sess.target.os {
+                Os::None => vec![],
                 // On macOS the aes, sha2 and sha3 features are enabled by default and ring
                 // fails to compile on macOS when they are not present.
-                "macos" => vec![sym::neon, sym::aes, sym::sha2, sym::sha3],
+                Os::MacOs => vec![sym::neon, sym::aes, sym::sha2, sym::sha3],
                 // AArch64 mandates Neon support
                 _ => vec![sym::neon],
             },
@@ -184,7 +184,7 @@ impl CodegenBackend for CraneliftCodegenBackend {
         // targets due to GCC using a different ABI than LLVM. Therefore `f16` and `f128`
         // won't be available when using a LLVM-built sysroot.
         let has_reliable_f16_f128 = !(sess.target.arch == Arch::X86_64
-            && sess.target.os == "windows"
+            && sess.target.os == Os::Windows
             && sess.target.env == Env::Gnu
             && sess.target.abi != Abi::Llvm);