Bug in bison 1.31 configure script

[Tony Leneis]

        I noticed there's a problem with the Bison 1.31 configure script
when run on Compaq Tru64 systems.  When configure determines that there
isn't a working malloc() function, it writes "#define malloc rpl_malloc"
to confdefs.h.  Later, when it tries to link the mmap() test program, it
fails because the program includes confdefs.h and uses malloc() (which is
now renamed to malloc_rpl().)

        I can think of four solutions, in decending order of preference:

(1) add this to the beginning of the mmap() test program:
    char *malloc_rpl(int n) { return malloc(n); }
    This is probably the cleanest and simplest solution.
(2) change the mmap() test program to use calloc() instead of malloc()
(3) reorder the configure tests so mmap() is tested before malloc()
(4) don't write the malloc define to confdefs.h (not sure what the
    consequences of this would be.)

-Tony