Build failure with stricter C compilers (e.g. GCC 14)

[thesamesam]

Describe the bug

Modern C compilers are becoming stricter with a variety of changes over the last year or so.

GCC 14 in particular (to be released in ~April 2024) fails to build gphoto2-2.2.58 like:

gphoto2-cmd-config.c: In function ‘set_config’:
gphoto2-cmd-config.c:74:42: error: passing argument 4 of ‘newCDKDialog’ from incompatible pointer type [-Wincompatible-pointer-types]
   74 |                                          msg, 4, buttons, 2,
      |                                          ^~~
      |                                          |
      |                                          const char **
In file included from /usr/include/cdk.h:40,
                 from gphoto2-cmd-config.c:36:
/usr/include/cdk/dialog.h:90:17: note: expected ‘char **’ but argument is of type ‘const char **’
   90 |                 CDK_CSTRING2    /* message */,
      |                 ^~~~~~~~~~~~
gphoto2-cmd-config.c:74:50: error: passing argument 6 of ‘newCDKDialog’ from incompatible pointer type [-Wincompatible-pointer-types]
   74 |                                          msg, 4, buttons, 2,
      |                                                  ^~~~~~~
      |                                                  |
      |                                                  const char **
/usr/include/cdk/dialog.h:92:17: note: expected ‘char **’ but argument is of type ‘const char **’
   92 |                 CDK_CSTRING2    /* buttons */,
      |                 ^~~~~~~~~~~~
gphoto2-cmd-config.c: In function ‘show_section’:
gphoto2-cmd-config.c:127:32: error: passing argument 8 of ‘newCDKScroll’ from incompatible pointer type [-Wincompatible-pointer-types]
  127 |                                (const char**)items, count, NUMBERS, A_REVERSE, TRUE, FALSE);
      |                                ^~~~~~~~~~~~~~~~~~~
      |                                |
      |                                const char **
/usr/include/cdk/scroll.h:82:17: note: expected ‘char **’ but argument is of type ‘const char **’
   82 |                 CDK_CSTRING2    /* itemList */,
      |                 ^~~~~~~~~~~~
gphoto2-cmd-config.c: In function ‘show_radio’:
gphoto2-cmd-config.c:321:53: error: passing argument 6 of ‘newCDKItemlist’ from incompatible pointer type [-Wincompatible-pointer-types]
  321 |                                title, _("Value: "), (const char**)items, count,
      |                                                     ^~~~~~~~~~~~~~~~~~~
      |                                                     |
      |                                                     const char **
/usr/include/cdk/itemlist.h:86:17: note: expected ‘char **’ but argument is of type ‘const char **’
   86 |                 CDK_CSTRING2    /* itemlist */,
      |                 ^~~~~~~~~~~~
gphoto2-cmd-config.c: In function ‘show_toggle’:
gphoto2-cmd-config.c:378:32: error: passing argument 6 of ‘newCDKItemlist’ from incompatible pointer type [-Wincompatible-pointer-types]
  378 |                                info, 2, 1 - value, TRUE, FALSE);
      |                                ^~~~
      |                                |
      |                                const char **
/usr/include/cdk/itemlist.h:86:17: note: expected ‘char **’ but argument is of type ‘const char **’
   86 |                 CDK_CSTRING2    /* itemlist */,
      |                 ^~~~~~~~~~~~
make[2]: *** [Makefile:797: gphoto2-gphoto2-cmd-config.o] Error 1

Originally reported downstream in Gentoo at https://bugs.gentoo.org/919279.

Name the camera N/A

libgphoto2 and gphoto2 version libgphoto2-2.5.1, gphoto2-2.5.28

To Reproduce Steps to reproduce the behavior: This can be emulated with -Werror=incompatible-pointer-types -Werror=implicit -Werror=int-conversion on an older GCC or Clang.

Similar to https://github.com/gphoto/libgphoto2/issues/941.