They issue, inst_* are subdirectories' Makefile vars, which compute
their values themselves. They don't seem to be initialized by configure
or top Makefile (even can't, as they are per-subdir), so top Makefile
passes empty values on command line to sub-Makefiles, which override
their own calculation of values, and causes them to execute commands
like "mkdir -p" (empty path).
I have no idea why *sometimes* it works (like when running
build-mingw32ce.sh), but it fails building w32api standalone.