[flang][driver] Make driver accept `-module-dir<value>`

[awarzynski]

Summary

-module-dir is Flang's equivalent for -J from GFortran (in fact,
-J is an alias for -module-dir in Flang). Currently, only
-module-dir <value> is accepted. However, -J (and other options for
specifying various paths) accepts -J <value> as well as -J<value>.
This patch makes sure that -module-dir behaves consistently with other
such flags.

[rovka]

Seems legit, thank you!

clang/include/clang/Driver/Options.td

 //===----------------------------------------------------------------------===//
 
 let Flags = [FC1Option, FlangOption, FlangOnlyOption] in {
 
 def cpp : Flag<["-"], "cpp">, Group<f_Group>,
   HelpText<"Enable predefined and command line preprocessor macros">;
 def nocpp : Flag<["-"], "nocpp">, Group<f_Group>,
   HelpText<"Disable predefined and command line preprocessor macros">;
-def module_dir : Separate<["-"], "module-dir">, MetaVarName<"<dir>">,
+def module_dir : JoinedOrSeparate<["-"], "module-dir">, MetaVarName<"<dir>">,
   HelpText<"Put MODULE files in <dir>">,
   DocBrief<[{This option specifies where to put .mod files for compiled modules.
 It is also added to the list of directories to be searched by an USE statement.
 The default is the current directory.}]>;
 
 def ffixed_form : Flag<["-"], "ffixed-form">, Group<f_Group>,
   HelpText<"Process source files in fixed form">;
 def ffree_form : Flag<["-"], "ffree-form">, Group<f_Group>,

flang/test/Driver/write-module.f90

 ! Checks that the module file:
 !   * is _saved_
 !   * is saved in the _directory specified by the user_
 ! We use `-fsyntax-only` as it stops after the semantic checks (the module file is generated when sema checks are run)
 
 !--------------------------
-! -module-dir
+! -module-dir <value>
+!--------------------------
+! RUN: rm -rf %t && mkdir -p %t/dir-flang
+! RUN: cd %t && %flang -fsyntax-only -module-dir %t/dir-flang %s
+! RUN: ls %t/dir-flang/testmodule.mod && not ls %t/testmodule.mod
+
+!--------------------------
+! -module-dir<value>
 !--------------------------
 ! RUN: rm -rf %t && mkdir -p %t/dir-flang
-! RUN: cd %t && %flang -fsyntax-only -module-dir %t/dir-flang %s
+! RUN: cd %t && %flang -fsyntax-only -module-dir%t/dir-flang %s
 ! RUN: ls %t/dir-flang/testmodule.mod && not ls %t/testmodule.mod
 
 !---------------------------
-! -J <dir> (i.e. with space)
+! -J <value>
 !---------------------------
 ! RUN: rm -rf %t && mkdir -p %t/dir-flang
 ! RUN: cd %t && %flang -fsyntax-only -J %t/dir-flang %s
 ! RUN: ls %t/dir-flang/testmodule.mod && not ls %t/testmodule.mod
 
 !------------------------------
-! -J<dir> (i.e. without space)
+! -J<value>
 !------------------------------
 ! RUN: rm -rf %t && mkdir -p %t/dir-flang
 ! RUN: cd %t && %flang -fsyntax-only -J%t/dir-flang %s
 ! RUN: ls %t/dir-flang/testmodule.mod && not ls %t/testmodule.mod
 
 module testmodule
   type::t2
   end type
 end