Add --no-detach to write to a separate debug file in the foreground

--detach is the default.

elf/cmdline.cc

@@ -85,6 +85,8 @@ Options:
   --defsym=SYMBOL=VALUE       Define a symbol alias
   --demangle                  Demangle C++ symbols in log messages (default)
     --no-demangle
+  --detach                    Create separate debug info file in the background (default)
+    --no-detach
   --enable-new-dtags          Emit DT_RUNPATH for --rpath (default)
     --disable-new-dtags       Emit DT_RPATH for --rpath
   --execute-only              Make executable segments unreadable
@@ -759,6 +761,10 @@ std::vector<std::string> parse_nonpositional_args(Context<E> &ctx) {
       ctx.arg.demangle = true;
     } else if (read_flag("no-demangle")) {
       ctx.arg.demangle = false;
+    } else if (read_flag("detach")) {
+      ctx.arg.detach = true;
+    } else if (read_flag("no-detach")) {
+      ctx.arg.detach = false;
     } else if (read_flag("default-symver")) {
       ctx.arg.default_symver = true;
     } else if (read_flag("noinhibit-exec")) {
@@ -1413,6 +1419,10 @@ std::vector<std::string> parse_nonpositional_args(Context<E> &ctx) {
   if (ctx.arg.shared && warn_shared_textrel)
     ctx.arg.warn_textrel = true;
 
+  // We don't want the background process to write to stdout
+  if (ctx.arg.stats || ctx.arg.perf)
+    ctx.arg.detach = false;
+
   ctx.arg.undefined.push_back(ctx.arg.entry);
 
   for (i64 i = 0; i < ctx.arg.defsyms.size(); i++) {

elf/mold.h

@@ -1740,6 +1740,7 @@ struct Context {
     bool color_diagnostics = false;
     bool default_symver = false;
     bool demangle = true;
+    bool detach = true;
     bool discard_all = false;
     bool discard_locals = false;
     bool eh_frame_hdr = true;

elf/passes.cc

@@ -3058,7 +3058,7 @@ void write_separate_debug_file(Context<E> &ctx) {
 
   // We want to write to the debug info file in background so that the
   // user doesn't have to wait for it to complete.
-  if (!ctx.arg.stats && !ctx.arg.perf)
+  if (ctx.arg.detach)
     notify_parent();
 
   // A debug info file contains all sections as the original file, though