Windows can create short names for directories that contain spaces in the name.

However, where short name creation was previously enabled by default, it no longer seems to be in recent version of Windows (the default setting is instead 'per volume', and the default for each volume is 'off').

Missing short names mean we can not create space-free paths in the various UTIL_MAKE_WINDOWS_SPACE_SAFE_* macros in make/autoconf/util_windows.m4, which leads to failures later on in the configuration with cryptic errors like "C compiler cannot create a simple executable", while the actual problem is a space in the path to said compiler.

We might want to consider checking that the output paths of these utility macros are actually space-free, and emit a warning or error otherwise. We should also add additional documentation about short names, and the short name creation setting to doc/building.md