./configure fails on windows when cmake is installed on a file path containing spaces

By default, cmake is installed in C:\Program Files\CMake, so this will fail on all default installations.

As far as I see, the culprit is in configure, line 1728: 
`(cd $LLVM_BUILD_DIR && eval "$CFG_CMAKE" $CMAKE_ARGS)`

A fix for this would be changing this line to 
`(cd $LLVM_BUILD_DIR && eval "\"$CFG_CMAKE\"" $CMAKE_ARGS)`
