RISC-V: Fix core type definitions and sizes

RISC-V port

fix idiom for setting stdio stream orientation to wide

the old idiom, f->mode |= f->mode+1, was adapted from the idiom for
setting byte orientation, f->mode |= f->mode-1, but the adaptation was
incorrect. unless the stream was alreasdy set byte-oriented, this code
incremented f->mode each time it was executed, which would eventually
lead to overflow. it could be fixed by changing it to f->mode |= 1,
but upcoming changes will require slightly more work at the time of
wide orientation, so it makes sense to just call fwide. as an
optimization in the single-character functions, fwide is only called
if the stream is not already wide-oriented.

fix failure of wide printf/scanf functions to set wide orientation

in some cases, these functions internally call a byte-based input or
output function before calling getwc/putwc, so they cannot rely on the
latter to set the orientation.

include cleanups: remove unused headers and add feature test macros

fix invalid %m format crash in wide scanf variants

the wide variant was missed in the previous commit.

fix uninitialized/stale use of alloc (%m modifier) flag in scanf

for conversion specifiers, alloc is always set when the specifier is
parsed. however, if scanf stops due to mismatching literal text,
either an uninitialized (if no conversions have been performed yet) or
stale (from the previous conversion) of the flag will be used,
possibly causing an invalid pointer to be passed to free when the
function returns.

fix scanf %c conversion wrongly storing a terminating null byte

this seems to have been a regression from the refactoring which added
the 'm' modifier.

implement 'm' modifier for wide scanf variants

refactor wide-char scanf string handling

this brings the wide version of the code into alignment with the
byte-based version, in preparation for adding support for the m
(malloc) modifier.

Add ABI compatability aliases.

GNU used several extensions that were incompatible with C99 and POSIX,
so they used alternate names for the standard functions.

The result is that we need these to run standards-conformant programs
that were linked with glibc.

use restrict everywhere it's required by c99 and/or posix 2008

to deal with the fact that the public headers may be used with pre-c99
compilers, __restrict is used in place of restrict, and defined
appropriately for any supported compiler. we also avoid the form
[restrict] since older versions of gcc rejected it due to a bug in the
original c99 standard, and instead use the form *restrict.

fix wide scanf's handling of input failure on %c, and simplify %[

fix failure to distinguish input/match failure in wide %[ scanf

this also includes a related fix for vswscanf's read function, which
was returning a spurious (uninitialized) character for empty strings.

fix broken %s and %[ with no width specifier in wide scanf

make wide scanf %[ respect width

fix wide scanf to respect field width for strings

introduce new wide scanf code and remove the last remnants of old scanf

at this point, strto* and all scanf family functions are using the new
unified integer and floating point parser/converter code.

the wide scanf is largely a wrapper for ordinary byte-based scanf;
since numbers can only contain ascii characters, only strings need to
be handled specially.

initial check-in, version 0.5.0