Add support for MinGW-w64 v8.0.0

[And sync with upstream.]

I've compared the crucial {msvcr*,ucrtbase}.def.in files against v7.0.0,
and they don't seem to feature any relevant changes.

See http://mingw-w64.org/doku.php/versions for the changelog; Direct3D
12 is one of the additions.

Corresponding upstream PR is dlang/installer#474.

Author: kinke

buildsdk.d

@@ -164,6 +164,10 @@ void sanitizeDef(string defFile)
         if (line == "ExtractIconW@")
             return ";ExtractIconW@";
 
+        // Apparent bugs in lib32/api-ms-win-*.def - missing stdcall params size suffix.
+        if (line[$-1] == '@' && baseName(defFile).startsWith("api-ms-win-"))
+            return ";" ~ line;
+
         return line;
     });
 }
@@ -207,7 +211,8 @@ void def2implib(string defFile)
     }
 
     const libFile = setExtension(defFile, ".lib");
-    runShell(`lib "/DEF:` ~ defFile ~ `" "/OUT:` ~ libFile ~ `"`);
+    const machine = x64 ? "X64" : "X86";
+    runShell(`lib "/DEF:` ~ defFile ~ `" /MACHINE:` ~ machine ~ ` "/OUT:` ~ libFile ~ `"`);
     std.file.remove(setExtension(defFile, ".exp"));
 }
 
@@ -378,7 +383,7 @@ void buildMsvcrt(string outDir)
         // compile some additional objects
         foreach (i; 0 .. 3)
             addObj(format!"msvcrt_stub%d.obj"(i), format!"/D_APPTYPE=%d msvcrt_stub.c"(i));
-        foreach (i; 0 .. 3)
+        foreach (i; 1 .. 3) // not needed for DLLs
             addObj(format!"msvcrt_stub_wide%d.obj"(i), format!"/D_APPTYPE=%d /D_UNICODE msvcrt_stub.c"(i));
         addObj("msvcrt_data.obj", "msvcrt_data.c");
         addObj("msvcrt_atexit.obj", "msvcrt_atexit.c");

legacy_stdio_definitions.c

@@ -36,4 +36,4 @@ void __legacy_stdio_definitions()
     vwscanf(NULL, NULL);
     wprintf(NULL);
     wscanf(NULL);
-}
+}