Different labels are no longer needed because the tables are now in
separate functions.

This splits a considerable chunk of code from the main vfprintf
function.  This will make it easier to remove the use of extend_alloca
from the positional argument handling code.

The second jump table will be moved to a separate function
in the next commit.

which is more efficient on all targets.

This constant will allow us to refer to the number of elements in
work_buffer across a function call boundary.

This makes the offset handling more explicit and avoids
cross-references between the jump tables.

This avoids preprocessor conditionals in function declarations.

BZ #16618

Under certain conditions wscanf can allocate too little memory for the
to-be-scanned arguments and overflow the allocated buffer.  The
implementation now correctly computes the required buffer size when
using malloc.

A regression test was added to tst-sscanf.

Due to tile missing a bunch of FP exception and rounding
support, the tests generate warnings.  These changes fix the
warnings by just not compiling some unused functions, and
adding some attribute ((unused)) tags.