The same source file cannot safely be used in different wscripts
with concurrency (if they were in the same wscript it works
.c.1.o .c.2.o, etc).
[387/764] c: libs/fst/vstwin.c -> build/libs/fst/vstwin.c.1.o
[731/764] c: libs/fst/vstwin.c -> build/libs/fst/vstwin.c.1.o
[746/764] cxxprogram: build/libs/fst/scanner.cc.1.o build/libs/fst/vstwin.c.1.o -> build/libs/fst/ardour-vst-scanner.exe
[750/764] cxxshlib: [...] build/libs/fst/vstwin.c.1.o [...] -> build/libs/ardour/ardour-3.dll
and about one every full moon (depending on concurrency) it failed:
missing file: 'build/libs/fst/vstwin.c.1.o'
20ea90a186