lld-link: Allow /? as option prefix, like -? allowed

[thakis]

Summary

link.exe seems to allow /?foo and -?foo in addition to /foo and -foo.

Since lld-link already supports the -?foo spelling, support /?foo as well.

[ruiu]

LGTM

lld/COFF/Options.td

 include "llvm/Option/OptParser.td"
 
 // link.exe accepts options starting with either a dash or a slash.
 
 // Flag that takes no arguments.
-class F<string name> : Flag<["/", "-", "-?"], name>;
+class F<string name> : Flag<["/", "-", "/?", "-?"], name>;
 
 // Flag that takes one argument after ":".
 class P<string name, string help> :
-      Joined<["/", "-", "-?"], name#":">, HelpText<help>;
+      Joined<["/", "-", "/?", "-?"], name#":">, HelpText<help>;
 
 // Boolean flag which can be suffixed by ":no". Using it unsuffixed turns the
 // flag on and using it suffixed by ":no" turns it off.
 multiclass B<string name, string help_on, string help_off> {
   def "" : F<name>, HelpText<help_on>;
   def _no : F<name#":no">, HelpText<help_off>;
 }
 

 def section : P<"section", "Specify section attributes">;
 def stack   : P<"stack", "Size of the stack">;
 def stub    : P<"stub", "Specify DOS stub file">;
 def subsystem : P<"subsystem", "Specify subsystem">;
 def timestamp : P<"timestamp", "Specify the PE header timestamp">;
 def version : P<"version", "Specify a version number in the PE header">;
 def wholearchive_file : P<"wholearchive", "Include all object files from this archive">;
 
-def disallowlib : Joined<["/", "-", "-?"], "disallowlib:">, Alias<nodefaultlib>;
+def disallowlib : Joined<["/", "-", "/?", "-?"], "disallowlib:">,
+    Alias<nodefaultlib>;
 
 def manifest : F<"manifest">, HelpText<"Create .manifest file">;
 def manifest_colon : P<
     "manifest",
     "NO disables manifest output; EMBED[,ID=#] embeds manifest as resource in the image">;
 def manifestuac : P<"manifestuac", "User access control">;
 def manifestfile : P<"manifestfile", "Manifest output path, with /manifest">;
 def manifestdependency : P<
     "manifestdependency",
     "Attributes for <dependency> element in manifest file; implies /manifest">;
 def manifestinput : P<
     "manifestinput",
     "Additional manifest inputs; only valid with /manifest:embed">;
 
 // We cannot use multiclass P because class name "incl" is different
 // from its command line option name. We do this because "include" is
 // a reserved keyword in tablegen.
-def incl : Joined<["/", "-"], "include:">,
+def incl : Joined<["/", "-", "/?", "-?"], "include:">,
     HelpText<"Force symbol to be added to symbol table as undefined one">;
 
 // "def" is also a keyword.
-def deffile : Joined<["/", "-"], "def:">,
+def deffile : Joined<["/", "-", "/?", "-?"], "def:">,
     HelpText<"Use module-definition file">;
 
 def debug : F<"debug">, HelpText<"Embed a symbol table in the image">;
 def debug_opt : P<"debug", "Embed a symbol table in the image with option">;
 def debugtype : P<"debugtype", "Debug Info Options">;
 def dll : F<"dll">, HelpText<"Create a DLL">;
 def driver : P<"driver", "Generate a Windows NT Kernel Mode Driver">;
 def nodefaultlib_all : F<"nodefaultlib">,

 // LLD extensions
 def exclude_all_symbols : F<"exclude-all-symbols">;
 def export_all_symbols : F<"export-all-symbols">;
 defm demangle : B<"demangle",
     "Demangle symbols in output (default)",
     "Do not demangle symbols in output">;
 def kill_at : F<"kill-at">;
 def lldmingw : F<"lldmingw">;
-def output_def : Joined<["/", "-"], "output-def:">;
+def output_def : Joined<["/", "-", "/?", "-?"], "output-def:">;
 def pdb_source_path : P<"pdbsourcepath",
                         "Base path used to make relative source file path absolute in PDB">;
 def rsp_quoting : Joined<["--"], "rsp-quoting=">,
   HelpText<"Quoting style for response files, 'windows' (default) or 'posix'">;
 def dash_dash_version : Flag<["--"], "version">,
   HelpText<"Print version information">;
 defm threads: B<"threads",
     "Run the linker multi-threaded (default)",
     "Do not run the linker multi-threaded">;
 
 // Flags for debugging
 def lldmap : F<"lldmap">;
-def lldmap_file : Joined<["/", "-"], "lldmap:">;
+def lldmap_file : Joined<["/", "-", "/?", "-?"], "lldmap:">;
 def show_timing : F<"time">;
 def summary : F<"summary">;
 
 //==============================================================================
 // The flags below do nothing. They are defined only for link.exe compatibility.
 //==============================================================================
 
-class QF<string name> : Joined<["/", "-", "-?"], name#":">;
+class QF<string name> : Joined<["/", "-", "/?", "-?"], name#":">;
 
 def ignoreidl : F<"ignoreidl">;
 def nologo : F<"nologo">;
 def throwingnew : F<"throwingnew">;
 def editandcontinue : F<"editandcontinue">;
 def fastfail : F<"fastfail">;
 
 def delay : QF<"delay">;
 def errorreport : QF<"errorreport">;
 def idlout : QF<"idlout">;
 def maxilksize : QF<"maxilksize">;
 def tlbid : QF<"tlbid">;
 def tlbout : QF<"tlbout">;
 def verbose_all : QF<"verbose">;
 def guardsym : QF<"guardsym">;