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_codegen_ssa/src/back/write.rs

@@ -99,6 +99,7 @@ pub struct ModuleConfig {
     pub emit_ir: bool,
     pub emit_asm: bool,
     pub emit_obj: EmitObj,
+    pub emit_thin_lto: bool,
     pub bc_cmdline: String,
 
     // Miscellaneous flags.  These are mostly copied from command-line
@@ -218,6 +219,7 @@ impl ModuleConfig {
                 false
             ),
             emit_obj,
+            emit_thin_lto: sess.opts.unstable_opts.emit_thin_lto,
             bc_cmdline: sess.target.bitcode_llvm_cmdline.to_string(),
 
             verify_llvm_ir: sess.verify_llvm_ir(),