[petsc-dev] Missing prototypes/feature test macros

[Jed Brown]

C89 and C99 do not define drand48 so it's not in a strict compile. C89
does not warn about missing function declarations so the test in
missing.py did not work. (This leads to confusing behavior where drand48
appears to always return 0.)

I have a stricter test in branch jed/missing-prototype, but it fails
because it creates duplicate definitions once the feature test macros
are defined. I'm not sure how to resolve this "dialect" issue. We should
probably not be creating the missing declarations when they can be
obtained via feature test macros.