Convert prototypes to ISO C90

[Bruno Haible]

Ulrich Drepper wrote:

> The reason why in many places K&R is used is to get exactly the right
> level of warnings re missing prototypes.  Leave it as is, there is no
> reason to change it.

Another reason is that
  - glibc/intl shouldn't diverge too much from gettext/intl, and
  - gettext/intl needs to support K&R because some packages (most notably GCC)
    have a copy of it included in their source and need to build with HP-UX cc
    and SunOS4 cc.

Bruno