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_codegen_llvm/src/llvm/ffi.rs

@@ -2176,6 +2176,7 @@ extern "C" {
         PrepareForThinLTO: bool,
         PGOGenPath: *const c_char,
         PGOUsePath: *const c_char,
+        PGOSampleUsePath: *const c_char,
     );
     pub fn LLVMRustAddLibraryInfo(
         PM: &PassManager<'a>,
@@ -2210,6 +2211,8 @@ extern "C" {
         PGOUsePath: *const c_char,
         InstrumentCoverage: bool,
         InstrumentGCOV: bool,
+        PGOSampleUsePath: *const c_char,
+        DebugInfoForProfiling: bool,
         llvm_selfprofiler: *mut c_void,
         begin_callback: SelfProfileBeforePassCallback,
         end_callback: SelfProfileAfterPassCallback,