Invert -Z generate-arange-section.

Because it uses `parse_bool` and defaults to true, it is actually
impossible to set it to false. Inverting its sense to `-Z
no-generate-arange-section` makes it usable.

src/librustc_codegen_llvm/llvm_util.rs

@@ -80,8 +80,7 @@ unsafe fn configure_llvm(sess: &Session) {
         if sess.print_llvm_passes() {
             add("-debug-pass=Structure", false);
         }
-
-        if sess.opts.debugging_opts.generate_arange_section {
+        if !sess.opts.debugging_opts.no_generate_arange_section {
             add("-generate-arange-section", false);
         }
         if get_major_version() >= 8 {

src/librustc_session/options.rs

@@ -815,8 +815,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "for every macro invocation, print its name and arguments"),
     debug_macros: bool = (false, parse_bool, [TRACKED],
         "emit line numbers debug info inside macros"),
-    generate_arange_section: bool = (true, parse_bool, [TRACKED],
-        "generate DWARF address ranges for faster lookups"),
+    no_generate_arange_section: bool = (false, parse_bool, [TRACKED],
+        "don't generate DWARF address ranges that give faster lookups"),
     keep_hygiene_data: bool = (false, parse_bool, [UNTRACKED],
         "don't clear the hygiene data after analysis"),
     keep_ast: bool = (false, parse_bool, [UNTRACKED],