[gimp] configure.ac, icons: check for the "gegl" binary

[Michael Natterer <mitch src gnome org>]

commit 44d5e7adcd6c8d3073a3cc9d71dee495ee58cf25
Author: Michael Natterer <mitch gimp org>
Date:   Mon Dec 21 00:21:17 2015 +0100

    configure.ac, icons: check for the "gegl" binary
    
    and use the found executable instead of hardcoding "gegl".

 configure.ac                        |    5 +++++
 icons/Symbolic-Inverted/Makefile.am |    3 ++-
 2 files changed, 7 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 190a2d0..bdbf535 100644
--- a/configure.ac
+++ b/configure.ac
@@ -628,6 +628,11 @@ else
 fi
 AC_MSG_RESULT($have_glib_2_43)
 
+AC_PATH_PROG(GEGL, gegl, no)
+if test "x$GEGL" = xno; then
+  AC_MSG_ERROR([Could not find gegl in your PATH])
+fi
+
 
 # Check for bind_textdomain_codeset, including -lintl if GLib brings it in.
 gimp_save_LIBS=$LIBS
diff --git a/icons/Symbolic-Inverted/Makefile.am b/icons/Symbolic-Inverted/Makefile.am
index 2f5dd96..4a05ee2 100644
--- a/icons/Symbolic-Inverted/Makefile.am
+++ b/icons/Symbolic-Inverted/Makefile.am
@@ -20,7 +20,8 @@ include $(top_srcdir)/icons/Symbolic/icon-list.mk
 
 %.png:
        mkdir -p `dirname $ `;
-       gegl -x "<gegl> \
+       $(GEGL) -x \
+       "<gegl> \
          <node operation='gegl:invert-linear'></node> \
          <node operation='gegl:load'> \
            <params> \