Recognize NOTINLINE in IR2-CONVERT-GLOBAL-VAR.

A known function #'FOO could be IR2-converted avoiding indirection
through the #<fdefn> of FOO. This is usually fine, but in some cases
causes undesirable behavior:

- Functions redefined by SB-SIMPLE-STREAMS should be invoked via
  an #<fdefn> because to do otherwise means that general-purpose code
  in file A which needs READ-CHAR is possibly incapable of operating
  on a SIMPLE-STREAM that is used in subsequently loaded file B.

- Functions such as LOAD and COMPILE-FILE which, though performance-
  sensitive in a broad sense, are not hugely impacted by saving a few
  instructions at the expense of being able to encapsulate them.
  For example the ASDF code fragment:
    (WITH-MUFFLED-COMPILER-CONDITIONS ()
      (APPLY 'COMPILE-FILE input-file ...) ...)
  produces a call to COMPILE-FILE that could otherwise never be TRACEd.

The 4 affected stream-related functions worked as-is because:
- the reader never uses (FOO #'READ-CHAR ...) etc
- even if it did, #<fdefn> elision doesn't happen in the cross-compiler