Emit an error if -Z instrument-xray is not supported

This is somewhat important because LLVM enables the pass based on
target architecture, but support by the target OS also matters.

For example, XRay attributes are processed by codegen for macOS
targets, but Apple linker fails to process relocations in XRay
data sections, so the feature as a whole is not supported there
for the time being.

compiler/rustc_error_messages/locales/en-US/session.ftl

@@ -25,6 +25,8 @@ session_profile_sample_use_file_does_not_exist = file `{$path}` passed to `-C pr
 
 session_target_requires_unwind_tables = target requires unwind tables, they cannot be disabled with `-C force-unwind-tables=no`
 
+session_instrumentation_not_supported = {$us} instrumentation is not supported for this target
+
 session_sanitizer_not_supported = {$us} sanitizer is not supported for this target
 
 session_sanitizers_not_supported = {$us} sanitizers are not supported for this target

compiler/rustc_session/src/errors.rs

@@ -71,6 +71,12 @@ pub struct ProfileSampleUseFileDoesNotExist<'a> {
 #[diag(session_target_requires_unwind_tables)]
 pub struct TargetRequiresUnwindTables;
 
+#[derive(Diagnostic)]
+#[diag(session_instrumentation_not_supported)]
+pub struct InstrumentationNotSupported {
+    pub us: String,
+}
+
 #[derive(Diagnostic)]
 #[diag(session_sanitizer_not_supported)]
 pub struct SanitizerNotSupported {

compiler/rustc_session/src/session.rs

@@ -1589,6 +1589,10 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
     {
         sess.emit_err(errors::SplitDebugInfoUnstablePlatform { debuginfo: sess.split_debuginfo() });
     }
+
+    if sess.opts.unstable_opts.instrument_xray.is_some() && !sess.target.options.supports_xray {
+        sess.emit_err(errors::InstrumentationNotSupported { us: "XRay".to_string() });
+    }
 }
 
 /// Holds data on the current incremental compilation session, if there is one.

tests/ui/instrument-xray/target-not-supported.rs

@@ -0,0 +1,9 @@
+// Verifies that `-Z instrument-xray` cannot be used with unsupported targets,
+//
+// needs-llvm-components: x86
+// compile-flags: -Z instrument-xray --target x86_64-apple-darwin
+// error-pattern: error: XRay instrumentation is not supported for this target
+
+#![feature(no_core)]
+#![no_core]
+#![no_main]

tests/ui/instrument-xray/target-not-supported.stderr

@@ -0,0 +1,4 @@
+error: XRay instrumentation is not supported for this target
+
+error: aborting due to previous error
+