libstdc++: Avoid bad_alloc exceptions when changing locales

libstdc++: Avoid bad_alloc exceptions when changing locales

For the --enable-clocale=generic configuration, the current code can
fail with a bad_alloc exception. This patch uses the nothrow version of
operator new and reports allocation failures by setting failbit in the
iostate variable.

	* config/locale/generic/c_locale.cc (__set_C_locale()): New function
	to set the "C" locale and return the name of the previous locale.
	(__convert_to_v<float>, __convert_to_v<double>)
	(__convert_to_v<long double>): Use __set_C_locale and set failbit on
	error.