documentation of AC_FUNC_ALLOCA and mingw-w64 compilers

[Vincent Torri]

Hey,

when using AC_FUNC_ALLOCA, the autoconf documentation says that one should 
paste some code. That code generates a warning because:

1) the doc says to paste

#elif defined __GNUC__
# define alloca __builtin_alloca

2) the MinGW-w64 compiler already defines alloca in malloc.h, that header 
files being included by stdlib.h because STDC_HEADERS is defined.

I don't know how to properly fix the doc. One solution would be:

#elif defined __GNUC__
# ifndef alloca
#  define alloca __builtin_alloca
# endif

what do you think ?

regards

Vincent Torri