Minor updates to Gaudi::Functional implementation

• do not explicitly specify details:: when it is not needed
• change a 'zip::const_range' into a 'zip::range' as the content is already const (and this avoids an internal compiler error downstream)
• define two macros to factor out the pragmas needed to exclude a false positive clang diagnostic, and update the existing exclusion to use these. Note that current clang trunk is fixed, see https://bugs.llvm.org/show_bug.cgi?id=42104, so starting with clang 9, the diagnostic should no longer have the false positive.