Consult libpng-config more consistently.

* configure.ac (edit_cflags): Move this up and to the top level,
so that PNG_CFLAGS can use it too.
(PNG_CFLAGS): New var.
(png_longjmp): Use PNG_CFLAGS when checking.
(LIBPNG): Be consistent about -lpng16 etc; e.g., don't use -lpng16
in some places and -lpng in others.  Test libpng-config's exit
status.  If it succeeds, use its output rather than appending -lz -lm.
* src/Makefile.in (PNG_CFLAGS): New var.
(ALL_CFLAGS): Use it.
* src/image.c [HAVE_PNG]: Don't worry about <libpng/png.h>, as
CFLAGS now handles this.

Fixes: debbugs:17339

1 files changed, 11 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index c79e1b01976..5b583849bd7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2014-05-02  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Consult libpng-config more consistently (Bug#17339).
+        * configure.ac (edit_cflags): Move this up and to the top level,
+        so that PNG_CFLAGS can use it too.
+        (PNG_CFLAGS): New var.
+        (png_longjmp): Use PNG_CFLAGS when checking.
+        (LIBPNG): Be consistent about -lpng16 etc; e.g., don't use -lpng16
+        in some places and -lpng in others.  Test libpng-config's exit
+        status.  If it succeeds, use its output rather than appending -lz -lm.
+
 2014-05-01  Glenn Morris  <rgm@gnu.org>
 
         * configure.ac (LIBPNG): Consult libpng-config for the precise