isnormal macro in fp.h broken on VMS.

It appears to have an extra closing parenthesis, which means any
use of it fails to compile.  Ouch:

  $ type abby_normal.c
  #include <fp.h>
  int main() {
      double pi = 3.414;
      int normality = isnormal(pi);
  }
  $ cc/float=ieee abby_normal

      int normality = isnormal(pi);
  ....................^
  %CC-E-NOSEMI, Missing ";".
  at line number 4 in file DSA23:[TEST]abby_normal.c;1

So don't use it but rather fall back to a solution based on
fp_classify.

Of course it's supposed to be in math.h, not fp.h, but I digress.