bug#30431: 27.0.50; "Work even if libpng is install in /usr/local" causes build failure

[Paul Eggert]

On 02/12/2018 11:13 AM, Glenn Morris wrote:
> AFAICS, the issue is that the CHECK_MODULES method sets PNG_LIBS (and
> PNG_CFLAGS), whereas the old method sets LIBPNG (and PNG_CFLAGS).
>
> So revert the reversion, and then apply eg:
>
> --- a/configure.ac
> +++ b/configure.ac
> @@ -3613,7 +3613,9 @@ elif test "${with_png}" != no; then
>       AC_CHECK_HEADER([png.h], [HAVE_PNG=yes])
>     elif test "${HAVE_X11}" = "yes" || test "${HAVE_W32}" = "yes"; then
>      EMACS_CHECK_MODULES([PNG], [libpng >= 1.0.0])
> -   if test $HAVE_PNG = no; then
> +   if test $HAVE_PNG = yes; then
> +    LIBPNG="$PNG_LIBS"
> +   else
>       # Test old way in case pkg-config doesn't have it (older machines).
>       AC_MSG_CHECKING([for libpng not configured by pkg-config])

Thanks, Glenn. Werner, does that work for you?