[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 #3 from John Simon <gcc at mailinator dot com> ---
The include chain is:

# 415 "../../gcc-8.1.0/gcc/system.h"
  <-- "/usr/include/signal.h"
    <-- "/usr/include/bits/sigcontext.h"
      <-- "/usr/include/asm/sigcontext.h"
         <-- "/usr/include/linux/compiler.h"