libstdc++: Add #error to some files that depend on a specific standard mode

Give more explicit errors if these files are not built with the correct
-std options.

libstdc++-v3/ChangeLog:

	* src/c++98/locale_init.cc: Require C++11.
	* src/c++98/localename.cc: Likewise.
	* src/c++98/misc-inst.cc: Require C++98.