Add missing includes to configure script (#658)

This is needed for gcc 14 and clang 16 as they both make implicit
function definitions a hard error.  In a configure script, this means
these tests will switch from passing to failing, which likely means
features will get unintentionally flipped as configure now thinks you
don't have support.

See: https://wiki.gentoo.org/wiki/Modern_C_porting
See: https://bugs.gentoo.org/931607

Co-authored-by: matoro <matoro@users.noreply.github.com>

autoconf/hercules.m4

@@ -380,6 +380,7 @@ AC_DEFUN([HC_CHECK_NEED_GETOPT_OPTRESET],
             AC_TRY_LINK(
                 [],
                 [
+                    #include <unistd.h>
                     extern int optreset;
                     optreset=1;
                     getopt(0,0,0);

configure.ac

@@ -1872,6 +1872,8 @@ if test "$GCC" = "yes"; then
                             -g -O2 -fomit-frame-pointer
                     */
 
+                    #include <string.h>
+
                     int foo ()
                     {
                         char a[50000+16];