MFC r263774:

Revert r263694, and apply a better fix to squelch unnecessary warnings
from clang about possible keywords being treated as identifiers for the
remainder of the translation unit (a.k.a. -Wkeyword-compat), when using
libstdc++ in combination with -Wsystem-headers.  This will not only fix
devd, but any C++ program using libstdc++.