Fix ProgramFiles path for 64-bit Windows installer

If we are building an 64bit installer on Windows we have to adjust the
Program Files path otherwise it uses the wrong Program Files (x86)
directory. Related CMake bug report
http://public.kitware.com/Bug/view.php?id=14211

Patch by Ismail Dönmez!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227999 91177308-0d34-0410-b5e6-96231b3b80d8

CMakeLists.txt

@@ -96,6 +96,9 @@ if(WIN32 AND NOT UNIX)
     "ExecWait '$INSTDIR/tools/msbuild/install.bat'")
   set(CPACK_NSIS_EXTRA_UNINSTALL_COMMANDS
     "ExecWait '$INSTDIR/tools/msbuild/uninstall.bat'")
+  if( CMAKE_CL_64 )
+    set(CPACK_NSIS_INSTALL_ROOT "$PROGRAMFILES64")
+  endif()
 endif()
 include(CPack)