[Bug c++/84744] cannot use glibc 2.27 with gcc 7.3

[schwab@linux-m68k.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84744

--- Comment #11 from Andreas Schwab <schwab@linux-m68k.org> ---
The glibc headers depend on the kernel UAPI headers, they need to be available
in the sysroot.