Use __c_wchar_t.

src/core/stdc/config.d

@@ -31,6 +31,10 @@ version (StdDdoc)
             alias ddoc_long = int;
             alias ddoc_ulong = uint;
         }
+        version (Posix)
+            alias ddoc_wchar_t = dchar;
+        else
+            alias ddoc_wchar_t = wchar;
     }
 
     /***
@@ -86,6 +90,12 @@ version (StdDdoc)
      * C++ compiler's `ptrdiff_t` type.
      */
     alias cpp_ptrdiff_t = ptrdiff_t;
+
+    /***
+     * Used for a character type that corresponds in size and mangling to the associated
+     * C++ compiler's `wchar_t` type.
+     */
+    alias wchar_t = ddoc_wchar_t;
 }
 else
 {
@@ -112,6 +122,9 @@ version (Windows)
 
     alias long  cpp_longlong;
     alias ulong cpp_ulonglong;
+
+    enum __c_wchar_t : wchar;
+    alias wchar_t = __c_wchar_t;
 }
 else version (Posix)
 {
@@ -143,6 +156,8 @@ else version (Posix)
     alias long  cpp_longlong;
     alias ulong cpp_ulonglong;
   }
+    enum __c_wchar_t : dchar;
+    alias wchar_t = __c_wchar_t;
 }
 
 version (CRuntime_Microsoft)

src/core/stdc/stddef.d

@@ -24,13 +24,4 @@ alias nullptr_t = typeof(null);
 
 // size_t and ptrdiff_t are defined in the object module.
 
-version (Windows)
-{
-    ///
-    alias wchar wchar_t;
-}
-else version (Posix)
-{
-    ///
-    alias dchar wchar_t;
-}
+public import core.stdc.config : wchar_t;

src/core/stdc/wchar_.d

@@ -83,7 +83,7 @@ else
 alias wchar_t wint_t;
 
 ///
-enum wchar_t WEOF = 0xFFFF;
+enum wchar_t WEOF = cast(wchar_t)0xFFFF;
 
 ///
 int fwprintf(FILE* stream, in wchar_t* format, ...);

src/rt/dmain2.d

@@ -599,7 +599,7 @@ extern (C) void _d_print_throwable(Throwable t)
                 len += written;
             }
 
-            typeof(ptr) get() { if (ptr) ptr[len] = 0; return ptr; }
+            typeof(ptr) get() { if (ptr) ptr[len] = '\0'; return ptr; }
 
             void free() { .free(ptr); }
         }