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++.

MFC after:	3 days
X-MFC-With:	r263694

contrib/libstdc++/include/bits/cpp_type_traits.h

@@ -80,6 +80,13 @@ _GLIBCXX_END_NAMESPACE
 
 _GLIBCXX_BEGIN_NAMESPACE(std)
 
+#ifdef __clang__
+// When using clang, suppress warnings about possible keywords (such as
+// __is_void, __is_pod, etc) being used as identifiers.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wkeyword-compat"
+#endif
+
 namespace __detail
 {
   // NB: g++ can not compile these if declared within the class
@@ -398,6 +405,10 @@ namespace __detail
     };
 #endif
 
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif
+
 _GLIBCXX_END_NAMESPACE
 
 #endif //_CPP_TYPE_TRAITS_H

sbin/devd/Makefile

@@ -13,7 +13,6 @@ LDADD=	-ll -lutil
 
 YFLAGS+=-v
 CFLAGS+=-I. -I${.CURDIR}
-CFLAGS.clang+=-Wno-keyword-compat
 
 CLEANFILES= y.output