BZ #15941: Fix INSTALL file regeneration failure with makeinfo 5.x

I have skipped regenerating the INSTALL file because we want to
continue using the 4.x generator for now.
Fix ChangeLog formatting
Remove unused variables in __stpncpy_chk
Accept output arguments to benchmark functions

This patch adds the ability to accept output arguments to functions
being benchmarked, by nesting the argument type in <> in the args
directive.  It includes the sincos implementation as an example, where
the function would have the following args directive:

  ## args: double:<double *>:<double *>

This simply adds a definition for a static variable whose pointer gets
passed into the function, so it's not yet possible to pass something
more complicated like a pre-allocated string or array.  That would be
a good feature to add if a function needs it.

The values in the input file will map only to the input arguments.  So
if I had a directive like this for a function foo:

  ## args: int:<int *>:int:<int *>

and I have a value list like this:

1, 2
3, 4
5, 6

then the function calls generated would be:

foo (1, &out1, 2, &out2);
foo (3, &out1, 4, &out2);
foo (5, &out1, 6, &out2);