Enable AutoFDO.

This largely involves implementing the options debug-info-for-profiling
and profile-sample-use and forwarding them on to LLVM.

AutoFDO can be used on x86-64 Linux like this:
rustc -O -Cdebug-info-for-profiling main.rs -o main
perf record -b ./main
create_llvm_prof --binary=main --out=code.prof
rustc -O -Cprofile-sample-use=code.prof main.rs -o main2

Now `main2` will have feedback directed optimization applied to it.

The create_llvm_prof tool can be obtained from this github repository:
https://github.com/google/autofdo

Fixes #64892.

compiler/rustc_session/src/config.rs

@@ -2009,6 +2009,15 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
         );
     }
 
+    if debugging_opts.profile_sample_use.is_some()
+        && (cg.profile_generate.enabled() || cg.profile_use.is_some())
+    {
+        early_error(
+            error_format,
+            "option `-Z profile-sample-use` cannot be used with `-C profile-generate` or `-C profile-use`",
+        );
+    }
+
     if debugging_opts.instrument_coverage.is_some()
         && debugging_opts.instrument_coverage != Some(InstrumentCoverage::Off)
     {