https://bugs.winehq.org/show_bug.cgi?id=56665
--- Comment #6 from Rafał Mużyło galtgendo@o2.pl --- ...you know, something seems fishy about your toolchain.
The test fails with 'fatal error: 'stddef.h' file not found'.
That header is provided by the compiler (both in gcc *and* llvm).
What are the chances you're using that '-isystem' switch wrong ?