Re: Configuring Emacs on Windows with autoconf

[Paul Eggert]

On 11/23/2012 11:38 AM, Eli Zaretskii wrote:
> how would configure know to use those
> lib/foo.c files for one particular build configuration?

Here's a common pattern:

  gl_FUNC_STRTOUMAX
  if test $ac_cv_func_strtoumax = no; then
    AC_LIBOBJ([strtoumax])
    gl_PREREQ_STRTOUMAX
  fi

The first macro tests whether strtoumax exists.
If it doesn't, the code invokes AC_LIBOBJ to say
that lib/strtoumax.o is needed, and invokes
gl_PREREQ_STRTOUMAX to configure all the stuff
that is needed to compile strtoumax.c.  If
strtoumax exists, the code doesn't compile strtoumax.c
and doesn't do the work necessary to configure it.

A different pattern is used when one must replace
a function rather than simply provide a substitute
when the function is missing.