Add windres wrapper

As is, the build calls windres/gcc instead of rc.exe/cvtres.exe.  We
add a minimalist wrapper to avoid that.  However, for some reason
`--escape` is passed to windres-options, what the wrapper can't handle,
so we disable in that script.

source/build-aux/windres

@@ -0,0 +1,33 @@
+#! /bin/sh
+
+OTHER_ARGS=()
+
+while [[ $# -gt 0 ]]; do
+  case $1 in
+    -i)
+      INPUT="`cygpath -w $2`"
+      shift
+      shift
+      ;;
+    --output-format=*)
+      if test "${1#*=}" != coff; then
+        echo "Unsupported output format ${1#*=}"
+        exit 1
+      fi
+      shift
+      ;;
+    -o)
+      OUTPUT="`cygpath -w $2`"
+      shift
+      shift
+      ;;
+    *)
+      OTHER_ARGS+=("$1")
+      shift
+      ;;
+  esac
+done
+
+rc.exe ${OTHER_ARGS[@]} -fo ${OUTPUT}.res ${INPUT}
+cvtres.exe -machine:${Platform} -out:${OUTPUT} ${OUTPUT}.res
+rm ${OUTPUT}.res

source/windows/windres-options

@@ -9,7 +9,7 @@
 
 escape=
 if test "$1" = "--escape"; then
-  escape=yes
+  escape=
   shift
 fi
 version="$1" # something like 2.0 or 2.17 or 2.17.3 or 2.17.3-pre3