[LLD] [MinGW] Add a LLD specific option -pdb

[mstorsjo]

Summary

This allows producing pdb debug info. This is a LLD specific option since GCC and GNU binutils doesn't support the PDB file format.

[ruiu]

LGTM

MinGW/Driver.cpp

bool mingw::link(ArrayRef<const char *> ArgsArr, raw_ostream &Diag) {
 
   if (auto *A = Args.getLastArg(OPT_o))
     Add("-out:" + StringRef(A->getValue()));
   else if (Args.hasArg(OPT_shared))
     Add("-out:a.dll");
   else
     Add("-out:a.exe");
 
+  if (auto *A = Args.getLastArg(OPT_pdb)) {
+    Add("-debug");
+    Add("-pdb:" + StringRef(A->getValue()));
+  } else if (!Args.hasArg(OPT_strip_all)) {
+    Add("-debug:dwarf");
+  }
+
   if (Args.hasArg(OPT_shared))
     Add("-dll");
   if (Args.hasArg(OPT_verbose))
     Add("-verbose");
   if (Args.hasArg(OPT_export_all_symbols))
     Add("-export-all-symbols");
-  if (!Args.hasArg(OPT_strip_all))
-    Add("-debug:dwarf");
   if (Args.hasArg(OPT_large_address_aware))
     Add("-largeaddressaware");
   if (Args.hasArg(OPT_kill_at))
     Add("-kill-at");
 
   if (Args.getLastArgValue(OPT_m) != "thumb2pe" &&
       Args.getLastArgValue(OPT_m) != "arm64pe" && !Args.hasArg(OPT_dynamicbase))
     Add("-dynamicbase:no");

MinGW/Options.td

 def whole_archive: F<"whole-archive">,
     HelpText<"Include all object files for following archives">;
 def verbose: F<"verbose">, HelpText<"Verbose mode">;
 
 // LLD specific options
 def _HASH_HASH_HASH : Flag<["-"], "###">,
     HelpText<"Print (but do not run) the commands to run for this compilation">;
 def mllvm: S<"mllvm">;
+def pdb: S<"pdb">, HelpText<"Specify output PDB debug information file">;
 def Xlink : J<"Xlink=">, MetaVarName<"<arg>">,
     HelpText<"Pass <arg> to the COFF linker">;
 
 // Currently stubs to avoid errors
 def Bdynamic: F<"Bdynamic">, HelpText<"Link against shared libraries">;
 def Bstatic: F<"Bstatic">, HelpText<"Do not link against shared libraries">;
 def O: Joined<["-"], "O">, HelpText<"Optimize output file size">;
 def build_id: F<"build-id">;

test/MinGW/driver.test

 
 RUN: ld.lld -### -m i386pep foo.o | FileCheck -check-prefix DEBUG %s
 DEBUG: -debug:dwarf
 
 RUN: ld.lld -### -m i386pep foo.o -s | FileCheck -check-prefix STRIP %s
 RUN: ld.lld -### -m i386pep foo.o --strip-all | FileCheck -check-prefix STRIP %s
 STRIP-NOT: -debug:dwarf
 
+RUN: ld.lld -### -m i386pep foo.o -pdb out.pdb | FileCheck -check-prefix PDB %s
+PDB: -debug -pdb:out.pdb
+PDB-NOT: -debug:dwarf
+
 RUN: ld.lld -### -m i386pep foo.o --large-address-aware | FileCheck -check-prefix LARGE-ADDRESS-AWARE %s
 LARGE-ADDRESS-AWARE: -largeaddressaware
 
 RUN: ld.lld -### -m i386pe foo.o | FileCheck -check-prefix DEFAULT-DISABLE-FLAGS %s
 RUN: ld.lld -### -m i386pep foo.o | FileCheck -check-prefix DEFAULT-DISABLE-FLAGS %s
 DEFAULT-DISABLE-FLAGS: -dynamicbase:no
 RUN: ld.lld -### -m i386pe --dynamicbase foo.o | FileCheck -check-prefix NO-DEFAULT-DISABLE-FLAGS %s
 RUN: ld.lld -### -m i386pep -dynamicbase foo.o | FileCheck -check-prefix NO-DEFAULT-DISABLE-FLAGS %s