[llvm-dlltool] Clarify parameters, simplify ArgList usage. NFC.

Add comments about unclear bool arguments to functions, switch to
hasArg instead of getLastArg for cases where we don't need to check
the argument's value.

Differential Revision: https://reviews.llvm.org/D152360

llvm/lib/ToolDrivers/llvm-dlltool/DlltoolDriver.cpp

@@ -166,7 +166,7 @@ int llvm::dlltoolDriverMain(llvm::ArrayRef<const char *> ArgsArr) {
   }
 
   Expected<COFFModuleDefinition> Def =
-      parseCOFFModuleDefinition(*MB, Machine, true);
+      parseCOFFModuleDefinition(*MB, Machine, /*MingwDef=*/true);
 
   if (!Def) {
     llvm::errs() << "error parsing definition\n"
@@ -197,7 +197,7 @@ int llvm::dlltoolDriverMain(llvm::ArrayRef<const char *> ArgsArr) {
     }
   }
 
-  if (Machine == IMAGE_FILE_MACHINE_I386 && Args.getLastArg(OPT_k)) {
+  if (Machine == IMAGE_FILE_MACHINE_I386 && Args.hasArg(OPT_k)) {
     for (COFFShortExport& E : Def->Exports) {
       if (!E.AliasTarget.empty() || (!E.Name.empty() && E.Name[0] == '?'))
         continue;
@@ -214,8 +214,8 @@ int llvm::dlltoolDriverMain(llvm::ArrayRef<const char *> ArgsArr) {
     }
   }
 
-  if (!Path.empty() &&
-      writeImportLibrary(Def->OutputFile, Path, Def->Exports, Machine, true))
+  if (!Path.empty() && writeImportLibrary(Def->OutputFile, Path, Def->Exports,
+                                          Machine, /*MinGW=*/true))
     return 1;
   return 0;
 }