[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 #2 from John Simon <gcc at mailinator dot com> ---
> Can you figure out who #defines noinline?

Sure. Using -E -dD pointed to "/usr/include/linux/compiler.h" which has:

```c
/*
 * From the GCC manual:
 *
 * Many functions do not examine any values except their arguments,
 * and have no effects except the return value.  Basically this is
 * just slightly more strict class than the `pure' attribute above,
 * since function is not allowed to read global memory.
 *
 * Note that a function that has pointer arguments and examines the
 * data pointed to must _not_ be declared `const'.  Likewise, a
 * function that calls a non-`const' function usually must not be
 * `const'.  It does not make sense for a `const' function to return
 * `void'.
 */
#ifndef __attribute_const__
# define __attribute_const__    /* unimplemented */
#endif

#ifndef noinline
#define noinline
#endif

#ifndef __always_inline
#define __always_inline inline
#endif
```