Windows: Add support for unicode command lines

Summary:
The MSVCRT deliberately sends main() code-page specific characters.
This isn't too useful to LLVM as we end up converting the arguments to
UTF-16 and subsequently attempt to use the result as, for example, a
file name.  Instead, we need to have the ability to access the Unicode
command line and transform it to UTF-8.

This has the distinct advantage over using the MSVC-specific wmain()
function as our entry point because:
 - It doesn't work on cygwin.
 - It only work on MinGW with caveats and only then on certain versions.
 - We get to keep our entry point as main(). :)

N.B.  This patch includes fixes to other parts of lib/Support/Windows
s.t. we would be able to take advantage of getting the Unicode paths.
E.G.  clang spawning clang -cc1 would want to give it Unicode arguments.

Reviewers: aaron.ballman, Bigcheese, rnk, ruiu

Reviewed By: rnk

CC: llvm-commits, ygao

Differential Revision: http://llvm-reviews.chandlerc.com/D1834

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192069 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Config/config.h.cmake

@@ -203,6 +203,9 @@
 /* Define to 1 if you have the `pthread' library (-lpthread). */
 #cmakedefine HAVE_LIBPTHREAD ${HAVE_LIBPTHREAD}
 
+/* Define to 1 if you have the `shell32' library (-lshell32). */
+#cmakedefine HAVE_LIBSHELL32 ${HAVE_LIBSHELL32}
+
 /* Define to 1 if you have the `udis86' library (-ludis86). */
 #undef HAVE_LIBUDIS86
 

include/llvm/Config/config.h.in

@@ -217,6 +217,9 @@
 /* Define to 1 if you have the `pthread' library (-lpthread). */
 #undef HAVE_LIBPTHREAD
 
+/* Define to 1 if you have the `shell32' library (-lshell32). */
+#undef HAVE_LIBSHELL32
+
 /* Define to 1 if you have the `udis86' library (-ludis86). */
 #undef HAVE_LIBUDIS86
 

include/llvm/Support/Process.h

@@ -25,8 +25,11 @@
 #ifndef LLVM_SUPPORT_PROCESS_H
 #define LLVM_SUPPORT_PROCESS_H
 
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/Config/llvm-config.h"
+#include "llvm/Support/Allocator.h"
+#include "llvm/Support/system_error.h"
 #include "llvm/Support/DataTypes.h"
 #include "llvm/Support/TimeValue.h"
 
@@ -168,6 +171,14 @@ public:
   // string. \arg Name is assumed to be in UTF-8 encoding too.
   static Optional<std::string> GetEnv(StringRef name);
 
+  /// This function returns a SmallVector containing the arguments passed from
+  /// the operating system to the program.  This function expects to be handed
+  /// the vector passed in from main.
+  static error_code
+  GetArgumentVector(SmallVectorImpl<const char *> &Args,
+                    ArrayRef<const char *> ArgsFromMain,
+                    SpecificBumpPtrAllocator<char> &ArgAllocator);
+
   /// This function determines if the standard input is connected directly
   /// to a user's input (keyboard probably), rather than coming from a file
   /// or pipe.