Allow vdprintf to work on non-blocking non-regular files (Rob Newberry)

include <sys/stat.h>

branches: 1.4.10;
Provide explicit LC_C_LOCALE accessor and drop the various NULL checks.
Provide LC_GLOBAL_LOCALE in a way that works with all locale functions.
Merge constant data used by the initial global locale and the C locale.
Drop function call layer for _current_locale() and directly return the
locale reference, not a pointer to it. Use protected access for global
variables, so that libc references can avoid the GOT overhead.

Add explicit locale versions for the printf family. Replace asprintf,
snprintf and sprintf with simple wrappers around the corresponding
va_list functions to reduce code duplication.

branches: 1.2.2; 1.2.8;
Retire varargs.h support. Move machine/stdarg.h logic into MI
sys/stdarg.h and expect compiler to provide proper builtins, defaulting
to the GCC interface. lint still has a special fallback.
Reduce abuse of _BSD_VA_LIST_ by defining __va_list by default and
derive va_list as required by standards.

add dprintf and vdprintf