Use Unicode command line when not using wmain() under Windows

While we use wmain() for the compilers that provide it since the changes of
bfa78c63b9, we still didn't handle Unicode
command line arguments not representable in the current Windows code page
correctly when using other compilers (e.g. MinGW).

Now use Win32 ::GetCommandLine() function for them and parse the command line
ourselves instead of relying on non-Unicode-friendly main() arguments which
can't represent arbitrary Unicode strings when not using UTF-8 (which is never
the case under Windows).

include/wx/app.h

@@ -798,17 +798,31 @@ public:
 // your compiler really, really wants main() to be in your main program (e.g.
 // hello.cpp). Now wxIMPLEMENT_APP should add this code if required.
 
-// For compilers that support it, prefer to use wmain() as this ensures any
-// Unicode strings can be passed as command line parameters and not just those
-// representable in the current locale.
-#if wxUSE_UNICODE && defined(__VISUALC__)
-    #define wxIMPLEMENT_WXWIN_MAIN_CONSOLE                                    \
-        int wmain(int argc, wchar_t **argv)                                   \
-        {                                                                     \
-            wxDISABLE_DEBUG_SUPPORT();                                        \
+// For compilers that support it, prefer to use wmain() and let the CRT parse
+// the command line for us, for the others parse it ourselves under Windows to
+// ensure that wxWidgets console applications accept arbitrary Unicode strings
+// as command line parameters and not just those representable in the current
+// locale (under Unix UTF-8, capable of representing any Unicode string, is
+// almost always used and there is no way to retrieve the Unicode command line
+// anyhow).
+#if wxUSE_UNICODE && defined(__WINDOWS__)
+    #ifdef __VISUALC__
+        #define wxIMPLEMENT_WXWIN_MAIN_CONSOLE                                \
+            int wmain(int argc, wchar_t **argv)                               \
+            {                                                                 \
+                wxDISABLE_DEBUG_SUPPORT();                                    \
                                                                               \
-            return wxEntry(argc, argv);                                       \
-        }
+                return wxEntry(argc, argv);                                   \
+            }
+    #else // No wmain(), use main() but don't trust its arguments.
+        #define wxIMPLEMENT_WXWIN_MAIN_CONSOLE                                \
+            int main(int, char **)                                            \
+            {                                                                 \
+                wxDISABLE_DEBUG_SUPPORT();                                    \
+                                                                              \
+                return wxEntry();                                             \
+            }
+    #endif
 #else // Use standard main()
     #define wxIMPLEMENT_WXWIN_MAIN_CONSOLE                                    \
         int main(int argc, char **argv)                                       \