[lld] Add --lto-emit-asm and alias --plugin-opt=emit-llvm to it (#97469)

Summary:
The LTO pass currently supporting emitting LTO via the
`--plugin-opt=emit-llvm` option. However, there is a very similar option
called `--lto-emit-asm`. This patch just makes the usage more
consistent and more obvious that emitting LLVM-IR is supported.

Author: jhuber6

lld/ELF/Driver.cpp

@@ -1269,7 +1269,7 @@ static void readConfigs(opt::InputArgList &args) {
   config->dynamicLinker = getDynamicLinker(args);
   config->ehFrameHdr =
       args.hasFlag(OPT_eh_frame_hdr, OPT_no_eh_frame_hdr, false);
-  config->emitLLVM = args.hasArg(OPT_plugin_opt_emit_llvm, false);
+  config->emitLLVM = args.hasArg(OPT_lto_emit_llvm);
   config->emitRelocs = args.hasArg(OPT_emit_relocs);
   config->enableNewDtags =
       args.hasFlag(OPT_enable_new_dtags, OPT_disable_new_dtags, true);

lld/ELF/Options.td

@@ -614,6 +614,8 @@ def lto_debug_pass_manager: FF<"lto-debug-pass-manager">,
   HelpText<"Debug new pass manager">;
 def lto_emit_asm: FF<"lto-emit-asm">,
   HelpText<"Emit assembly code">;
+def lto_emit_llvm: FF<"lto-emit-llvm">,
+  HelpText<"Emit LLVM-IR bitcode">;
 def lto_newpm_passes: JJ<"lto-newpm-passes=">,
   HelpText<"Passes to run during LTO">;
 def lto_O: JJ<"lto-O">, MetaVarName<"<opt-level>">,
@@ -695,7 +697,8 @@ def plugin_opt_dwo_dir_eq: J<"plugin-opt=dwo_dir=">,
   HelpText<"Directory to store .dwo files when LTO and debug fission are used">;
 def plugin_opt_emit_asm: F<"plugin-opt=emit-asm">,
   Alias<lto_emit_asm>, HelpText<"Alias for --lto-emit-asm">;
-def plugin_opt_emit_llvm: F<"plugin-opt=emit-llvm">;
+def plugin_opt_emit_llvm: F<"plugin-opt=emit-llvm">,
+  Alias<lto_emit_llvm>, HelpText<"Alias for --lto-emit-llvm">;
 def: J<"plugin-opt=jobs=">, Alias<thinlto_jobs_eq>, HelpText<"Alias for --thinlto-jobs=">;
 def: J<"plugin-opt=lto-partitions=">, Alias<lto_partitions>, HelpText<"Alias for --lto-partitions">;
 def plugin_opt_mcpu_eq: J<"plugin-opt=mcpu=">;

lld/test/ELF/lto/emit-llvm.ll

@@ -7,6 +7,7 @@
 ;; Regression test for D112297: bitcode writer used to crash when
 ;; --plugin-opt=emit-llvmis enabled and the output is /dev/null.
 ; RUN: ld.lld --plugin-opt=emit-llvm -mllvm -bitcode-flush-threshold=0 -o /dev/null %t.o
+; RUN: ld.lld --lto-emit-llvm -mllvm -bitcode-flush-threshold=0 -o /dev/null %t.o
 
 ; CHECK: define internal void @main()