THRIFT-4184: fix appveyor build issue with escaped character sequence in boost path

This closes #1259
diff --git a/build/appveyor/cl_setenv.bat b/build/appveyor/cl_setenv.bat
index c1b956c..e80d6b5 100644
--- a/build/appveyor/cl_setenv.bat
+++ b/build/appveyor/cl_setenv.bat
@@ -21,7 +21,7 @@
 ) ELSE IF "%PROFILE%" == "MSVC2015" (
   CALL "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" %PLATFORM%
 ) ELSE IF "%PROFILE%" == "MSVC2017" (
-  CALL "C:\Program Files (x86)\Microsoft Visual Studio 15.0\VC\vcvarsall.bat" %PLATFORM%
+  CALL "C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\Common7\Tools\VsDevCmd.bat" %PLATFORM%
 ) ELSE IF "%PROFILE%" == "MINGW" (
   SET MSYS2_PATH_TYPE=stock
 ) ELSE IF "%PROFILE%" == "MSYS" (
@@ -44,8 +44,9 @@
 SET NORM_PLATFORM=%PLATFORM:~-2,2%
 IF "%NORM_PLATFORM%" == "86" (SET NORM_PLATFORM=32)
 
-SET BOOST_ROOT=C:\Libraries\boost_%BOOST_VERSION:.=_%
-SET BOOST_LIBRARYDIR=%BOOST_ROOT%\lib%NORM_PLATFORM%-msvc-%COMPILER:~-3,2%.0
+:: FindBoost needs forward slashes so cmake doesn't see something as an escaped character
+SET BOOST_ROOT=C:/Libraries/boost_%BOOST_VERSION:.=_%
+SET BOOST_LIBRARYDIR=%BOOST_ROOT%/lib%NORM_PLATFORM%-msvc-%COMPILER:~-3,2%.0
 SET OPENSSL_ROOT=C:\OpenSSL-Win%NORM_PLATFORM%
 SET WIN3P=%APPVEYOR_BUILD_FOLDER%\thirdparty