libstdc++: std::ctype fixes for recent versions of NetBSD

libstdc++: std::ctype fixes for recent versions of NetBSD

This removes support for EOL versions of NetBSD and syncs the
definitions with patches from NetBSD upstream.

The only change here that isn't from upstream is to use _CTYPE_BL for
the isblank class, which is correct but wasn't previously done either in
FSF GCC or the NetBSD packages.

2020-01-16  Kai-Uwe Eckhardt  <kuehro@gmx.de>
	    Matthew Bauer  <mjbauer95@gmail.com>
	    Jonathan Wakely  <jwakely@redhat.com>

	PR bootstrap/64271 (partial)
	* config/os/bsd/netbsd/ctype_base.h (ctype_base::mask): Change type
	to unsigned short.
	(ctype_base::alpha, ctype_base::digit, ctype_base::xdigit)
	(ctype_base::print, ctype_base::graph, ctype_base::alnum): Sync
	definitions with NetBSD upstream.
	(ctype_base::blank): Use _CTYPE_BL.
	* config/os/bsd/netbsd/ctype_configure_char.cc (_C_ctype_): Remove
	Declaration.
	(ctype<char>::classic_table): Use _C_ctype_tab_ instead of _C_ctype_.
	(ctype<char>::do_toupper, ctype<char>::do_tolower): Cast char
	parameters to unsigned char.
	* config/os/bsd/netbsd/ctype_inline.h (ctype<char>::is): Likewise.