__DBL_HAS_DENORM__ et al required in recent libstdc++

[Tim Prince <timothyprince@xxxxxxxxxxxxx>]

Builds of gcc-4.3 libstdc++ on cygwin have begun failing with these 
undefined symbols for FLT,DBL,LDBL in std_limits.h.  I don't find any 
explanation of it.  Is it a particular problem for cygwin, given that 
the include files for LDBL are incomplete, and don't distinguish between 
DBL and LDBL?  Are these values intended to reflect options such as 
-ffast-math and -mfpmath which would affect use of subnormals (formerly 
called denorm)?