Call _M_extract_* functions family through temporary int objects, so
it doesn't convert from lvalue to rvalue through a temporary in AVR
because of the incompatible types used in AVR-Libc.

This fixes compilation errors with AVR-Libc while compiling libstdc++
for AVR target.

2017-01-10  Felipe Magno de Almeida <felipe@expertisesolutions.com.br>

	* include/bits/locale_facets_nonio.tcc
	(time_get::_M_extract_via_format): Avoid compilation errors with
	non-standard struct tm.

From-SVN: r244271