Newer compilers default to GNU11, a C11 dialect. Some software however
is unprepared for this or has wrong compatibility checks. What happens
is that some software will for compatibility with C89
#define inline
before inclusion of a standard header, which is undefined behaviour in
C99 and above (C99/C11 7.1.2/4), as inline is a keyword.
If any libc headers that are then included via #include_next provide an
__inline macro definition (current musl does this if C++ or C99 and
above is detected) like the following
#define __inline inline
this results in any __inline token to be preprocessed away.
This breaks use of __builtin_va_arg_pack() in our stdio.h at
compile-time as it can only be used in always inlined functions. The
function attributes __always_inline__ and __gnu_inline__ themselves
require an inline specifier on the function to be applied.
