alloca() declaration

[Anders Magnusson <ragge%ludd.ltu.se@localhost>]

I noticed that there is a difference between whether alloca() is in libc 
or not for our ports.
arm, i386, m68k, vax, amd64 has the functions, others not.

Also, the stuff in is not correct either:

#if defined(alloca) && (alloca == __builtin_alloca) && \
    defined(__GNUC__) && (__GNUC__ < 2)
void    *alloca(int);     /* built-in for gcc */
#elif defined(__PCC__) && !defined(__GNUC__)
#define alloca(size) __builtin_alloca(size)
#else
void    *alloca(size_t);
#endif /* __GNUC__ */

besides the fact that string comparison is not possible in cpp this 
would in fact usually just end up in declaring alloca().

This means that alloca won't be available if using gcc -std=c99 on a 
bunch of ports, which is not the desired behavior.

One way to solve this would be to replace the stuff above with:
#if defined(__GNUC__)
#define alloca(size) __builtin_alloca(size)
#endif

so that gcc always uses the builtin alloca.

Comments?

-- Ragge