rustc: add ability to output regular LTO bitcode modules

Adding the option to control from rustc CLI
if the resulted ".o" bitcode module files are with
thinLTO info or regular LTO info.

Allows using "-lto-embed-bitcode=optimized" during linkage
correctly.

Signed-off-by: Ziv Dunkelman <ziv.dunkelman@nextsilicon.com>

compiler/rustc_session/src/options.rs

@@ -1277,6 +1277,8 @@ options! {
         "version of DWARF debug information to emit (default: 2 or 4, depending on platform)"),
     emit_stack_sizes: bool = (false, parse_bool, [UNTRACKED],
         "emit a section containing stack size metadata (default: no)"),
+    emit_thin_lto: bool = (true, parse_bool, [TRACKED],
+        "emit the bc module with thin LTO info (default: yes)"),
     fewer_names: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "reduce memory use by retaining fewer names within compilation artifacts (LLVM-IR) \
         (default: no)"),