Remove rarely used -Zdisable_instrumentation_preinliner flag.

The same effect can be achieved by `-Cllvm-args=-disable-preinline`.

src/librustc_codegen_llvm/llvm_util.rs

@@ -80,9 +80,7 @@ unsafe fn configure_llvm(sess: &Session) {
         add("rustc", true); // fake program name
         if sess.time_llvm_passes() { add("-time-passes", false); }
         if sess.print_llvm_passes() { add("-debug-pass=Structure", false); }
-        if sess.opts.debugging_opts.disable_instrumentation_preinliner {
-            add("-disable-preinline", false);
-        }
+
         if sess.opts.debugging_opts.generate_arange_section {
             add("-generate-arange-section", false);
         }

src/librustc_session/options.rs

@@ -866,8 +866,6 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "extra arguments to prepend to the linker invocation (space separated)"),
     profile: bool = (false, parse_bool, [TRACKED],
                      "insert profiling code"),
-    disable_instrumentation_preinliner: bool = (false, parse_bool, [TRACKED],
-        "Disable the instrumentation pre-inliner, useful for profiling / PGO."),
     relro_level: Option<RelroLevel> = (None, parse_relro_level, [TRACKED],
         "choose which RELRO level to use"),
     nll_facts: bool = (false, parse_bool, [UNTRACKED],