Upgrade to AppVeyor vs2017 image

[jwillemsen]

We should upgrade to AppVeyor vs2017 support but looks we have a perl issue. On the vs2017 image we don't get a normal perl (see https://www.appveyor.com/docs/build-environment/#perl), we probably get a Cygwin version which fails to work, MPC doesn't work

Build started
git clone -q --depth=15 https://github.com/DOCGroup/ACE_TAO.git C:\projects\ace-tao-lc76l
git fetch -q origin +refs/pull/391/merge:
git checkout -qf FETCH_HEAD
Running Install scripts
mkdir ext && cd ext
git clone --depth 1 git://github.com/DOCGroup/MPC.git
Cloning into 'MPC'...
cd ..
set MPC_ROOT=%CD%\ext\MPC
set ACE_ROOT=%CD%\ACE
set TAO_ROOT=%CD%\TAO
set PATH=%ACE_ROOT%\lib:%PATH%
$CONTENT='#include "ace/config-win32.h"'
$CONTENT > ACE\ace\config.h
call "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvarsall.bat" amd64
**********************************************************************
** Visual Studio 2017 Developer Command Prompt v15.0.26228.12
** Copyright (c) 2017 Microsoft Corporation
**********************************************************************
[vcvarsall.bat] Environment initialized for: 'x64'
call perl %CD%\ACE\bin\mwc.pl -type vs2017 %CD%\TAO\TAO_ACE.mwc
MPC_ROOT was set to C:\projects\ace-tao-lc76l\ext\MPC.
Generating 'vs2017' output using C:/projects/ace-tao-lc76l/TAO/TAO_ACE.mwc
ace_xtreactor.mpc: line 2:
ERROR: Unable to locate parent: ace_xt
TAO_ACE.mwc: line 22:
ERROR: Unable to process C:/projects/ace-tao-lc76l/ACE/ace/XtReactor/ace_xtreactor.mpc
ERROR: Unable to process: TAO_ACE.mwc
Command exited with code 1

[jwillemsen]

Fixed with PR #398

[jwillemsen]

Fixed