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
Fix comments: STRING-INPUT-STREAM-STRING is read-only and simple.
Freeze INTERPRETED-FUNCTION type
Add expected results for #\` expansion incl. pvk's change f2503917.

All will pass with the new implementation, pending commit.
Fix indentation
Fix &OPTIONAL + &REST handling in FIND-OPTIONAL-DISPATCH-TYPES

Previously, certain combinations of proclamations and definitions, such as

  (declaim (ftype (function (symbol &optional t &rest t)) foo))
  (defun foo (x &optional y &rest z))

lead to bogus STYLE-WARNINGs about mismatches between proclamation and
definition:

  The definition has one optional arg, but proclamation has zero.

This was caused by the simplifications of function types

     (function (symbol &optional t &rest t) symbol)
  ~> (function (symbol &rest t) symbol)

which FIND-OPTIONAL-DISPATCH-TYPES did not take into account.
Fix ftype proclamation and definition of ASSERT[-SYMBOL-HOME]-PACKAGE-UNLOCKED

* The ftype proclamation for ASSERT-SYMBOL-HOME-PACKAGE-UNLOCKED could
  be tightened.

* The lambda-list of the ASSERT-SYMBOL-HOME-PACKAGE-UNLOCKED stub in
  src/code/cross-misc.lisp differed from the ftype proclamation and the
  actual implementation. Fixing it exposed the bug fixed in c6f864d.
Fix typo in NEWS

Reported-by: Douglas Katzman
Fix sigtrap_handler on ARM.

The previous change removed the undefined instruction handling,
breaking many things.
Store unibyte mapping tables more densely by specializing the vectors.

Incidentally, get the cross-compiler to dump SIGNED-BYTE arrays.
Merge branch 'master' into unicode-algorithms
Adds MATH-P to SB-UNICODE