[libc++] Fix usage of 'exclude_from_explicit_instantiation' attribute on local class members (#89377)

#88777 adds a warning for when the `exclude_from_explicit_instantiation`
attribute is applied to local classes and members thereof. This patch
addresses the few instances of `exclude_from_explicit_instantiation`
being applied to local class members in libc++.

GitOrigin-RevId: ab22504479cb7b8985855aa2f2c851390bc1d167
2 files changed