r350739 try #2

For some inexplicable reason, C++ compilers reject the -Wno- flag, and also
(ab)use CWARNFLAGS.

Reported by:	imp

Author: cemeyer

share/mk/bsd.sys.mk

@@ -187,7 +187,7 @@ CWARNFLAGS+=	-Wno-unknown-pragmas
 .endif # IGNORE_PRAGMA
 
 # This warning is utter nonsense
-CWARNFLAGS+=	-Wno-format-zero-length
+CFLAGS+=	-Wno-format-zero-length
 
 # We need this conditional because many places that use it
 # only enable it for some files with CLFAGS.$FILE+=${CLANG_NO_IAS}.