Minimize printf/scanf size on platforms that don't need C99.

Minimize printf/scanf size on platforms that don't need C99.
* acconfig.h (_WANT_IO_C99_FORMATS): New macro.
* newlib.hin (_WANT_IO_C99_FORMATS): Likewise.
* configure.in (newlib-io-c99-formats): New configure option.
(_WANT_IO_C99_FORMATS): Define appropriately.
* configure.host (*-linux*, cygwin): Default c99-formats to yes.
* libc/stdio/vfprintf.c (_VFPRINTF_R) [!_WANT_IO_C99_FORMATS]:
Cripple ' flag; hh, z, j, t sizes; a, A, F, C, S specifiers.
* libc/stdio/vfscanf.c (_VFSCANF_R) [!_WANT_IO_C99_FORMATS]:
Likewise.
* configure: Regenerate.