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

3 files changed, 10 insertions, 4 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 12a0cd63dc0..29fb2dd1edf 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,11 @@
+2014-05-02  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Consult libpng-config more consistently (Bug#17339).
+        * Makefile.in (PNG_CFLAGS): New var.
+        (ALL_CFLAGS): Use it.
+        * image.c [HAVE_PNG]: Don't worry about <libpng/png.h>, as
+        CFLAGS now handles this.
+
 2014-05-01  Glenn Morris  <rgm@gnu.org>
 
         * floatfns.c (Fisnan):
diff --git a/src/Makefile.in b/src/Makefile.in
index 388923596c9..c35e38bb290 100644
--- a/src/Makefile.in
+++ b/src/Makefile.in
@@ -77,6 +77,7 @@ C_SWITCH_MACHINE=@C_SWITCH_MACHINE@
 C_SWITCH_SYSTEM=@C_SWITCH_SYSTEM@
 
 GNUSTEP_CFLAGS=@GNUSTEP_CFLAGS@
+PNG_CFLAGS=@PNG_CFLAGS@
 
 ## Define C_SWITCH_X_SITE to contain any special flags your compiler
 ## may need to deal with X Windows.  For instance, if you've defined
@@ -325,6 +326,7 @@ ALL_CFLAGS=-Demacs $(MYCPPFLAGS) -I. -I$(srcdir) \
   -I$(lib) -I$(srcdir)/../lib \
   $(C_SWITCH_MACHINE) $(C_SWITCH_SYSTEM) $(C_SWITCH_X_SITE) \
   $(GNUSTEP_CFLAGS) $(CFLAGS_SOUND) $(RSVG_CFLAGS) $(IMAGEMAGICK_CFLAGS) \
+  $(PNG_CFLAGS) \
   $(LIBXML2_CFLAGS) $(DBUS_CFLAGS) $(XRANDR_CFLAGS) $(XINERAMA_CFLAGS) \
   $(SETTINGS_CFLAGS) $(FREETYPE_CFLAGS) $(FONTCONFIG_CFLAGS) \
   $(LIBOTF_CFLAGS) $(M17N_FLT_CFLAGS) $(DEPFLAGS) \
diff --git a/src/image.c b/src/image.c
index 4133aaa7621..dcbe5942b32 100644
--- a/src/image.c
+++ b/src/image.c
@@ -22,12 +22,8 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <unistd.h>
 
 #ifdef HAVE_PNG
-#if defined HAVE_LIBPNG_PNG_H
-# include <libpng/png.h>
-#else
 # include <png.h>
 #endif
-#endif
 
 #include <setjmp.h>
 #include <c-ctype.h>