Add internal implementations for argp.h, err.h, and error.h functions

Add internal implementations for argp.h, err.h, and error.h functions

Since the introduction of explicit flags in the internal implementation
of the printf family of functions, the 'mode' parameter can be used to
select which format long double parameters have (with the mode flag:
PRINTF_LDBL_IS_DBL).  This patch uses this feature in the implementation
of some functions in argp.h, err.h, and error.h (only those that take a
format string and positional parameters).  Future patches will add
support for 'nldbl' and 'ieee128' versions of these functions.

Tested for powerpc64le and x86_64.