Stabilize -Z strip as -C strip

Leave -Z strip available temporarily as an alias, to avoid breaking
cargo until cargo transitions to using -C strip. (If the user passes
both, the -C version wins.)

compiler/rustc_session/src/config.rs

@@ -37,7 +37,7 @@ use std::iter::{self, FromIterator};
 use std::path::{Path, PathBuf};
 use std::str::{self, FromStr};
 
-/// The different settings that the `-Z strip` flag can have.
+/// The different settings that the `-C strip` flag can have.
 #[derive(Clone, Copy, PartialEq, Hash, Debug)]
 pub enum Strip {
     /// Do not strip at all.

compiler/rustc_session/src/options.rs

@@ -1015,6 +1015,8 @@ options! {
         "use soft float ABI (*eabihf targets only) (default: no)"),
     split_debuginfo: Option<SplitDebuginfo> = (None, parse_split_debuginfo, [TRACKED],
         "how to handle split-debuginfo, a platform-specific option"),
+    strip: Strip = (Strip::None, parse_strip, [UNTRACKED],
+        "tell the linker which information to strip (`none` (default), `debuginfo` or `symbols`)"),
     target_cpu: Option<String> = (None, parse_opt_string, [TRACKED],
         "select target processor (`rustc --print target-cpus` for details)"),
     target_feature: String = (String::new(), parse_target_feature, [TRACKED],