Removed the -Wunsuffixed-float-constants warning from the gnu-flags
script. The warnings that this generates cannot easily be resolved in
platform-independent C code since gnu expects the non-standard (gnu)
'D' suffix for double constants.

It's still technically useful for catching float and long double
constants, but should probably be enabled by developers on an
as-needed basis for that purpose so the spurious warnings are
avoided.

Tested on a local linux VM with gcc 4.8.2. This is a very minor change.