[Bug bootstrap/85921] /gcc/c-family/c-warn.c fails to build

[gcc at mailinator dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85921

--- Comment #8 from John Simon <gcc at mailinator dot com> ---
https://gcc.gnu.org/install/ doesn't say anything about make headers_install.

How/Where to do this?
If this is appropriate then it is much better than manually patching anything.

In this case I'd still suggest to check in gcc's configure if the headers are
reasonable, with the most simple check

AC_MSG_CHECKING([for reasonable kernel headers])
AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
        #include "gcc/system.h"
        #if defined noinline
        choke me
        #endif
]])],
[],
[AC_MSG_ERROR([system headers define noinline])])