Don't warn for -Wstatic-in-inline if the used function is also inline.

Also, don't warn if the used function is __attribute__((const)), in which case
it's not supposed to use global variables anyway.

The inline-in-inline thing is a heuristic, and one that's possibly incorrect
fairly often because the function being inlined could definitely use global
variables. However, even some C standard library functions are written using
other (trivial) static-inline functions in the headers, and we definitely don't
want to be warning on that (or on anything that /uses/ these trivial inline
functions). So we're using "inlined" as a marker for "fairly trivial".

(Note that __attribute__((pure)) does /not/ guarantee safety like ((const),
because ((const)) does not guarantee that global variables are not being used,
and the warning is about globals not being shared across TUs.)

llvm-svn: 158898