place to instantiate a template missing from libstdc++-v3.a

[Jan Beulich]

On a platform using config/locale/generic/c_locale.cc and not having any
of strtof(), finitef(), and finite(), the code makes use of isinf(),
which is forced to be a template under certain additional conditions
that are also met for this target. Since everything gets compiled with
-fno-implicit-templates, an instantiation of this template must be added
somewhere, but to me adding it to config/locale/generic/c_locale.cc
itself seems to be a rather bad idea. Hence I'd like to understand where
the proper place for adding such an explicit instantiation would be.

Thanks, Jan