[gegl] Fix build with slibtool.

[Øyvind "pippin" Kolås <ok src gnome org>]

commit 6931adcd7cb5474c2c00e6086b00f0c7fa4b7e5c
Author: orbea <orbea fredslev dk>
Date:   Fri Jun 1 14:05:34 2018 -0700

    Fix build with slibtool.
    
    When building gegl with slibtool instead of libtool the build fails.
    
      /usr/bin/ld: cannot find -lpoly2tri-c
    
    I bisected this issue to the follow commit and it appears to be a gegl
    issue.
    
    https://gitlab.gnome.org/GNOME/gegl/commit/73c5eba7ce11beba0e164fd27156ee224774da18

 operations/seamless-clone/Makefile.am | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/operations/seamless-clone/Makefile.am b/operations/seamless-clone/Makefile.am
index e1dfc9121..9abe6ff8e 100644
--- a/operations/seamless-clone/Makefile.am
+++ b/operations/seamless-clone/Makefile.am
@@ -4,7 +4,7 @@ include $(top_srcdir)/operations/Makefile-common.am
 # Seamless cloning operations #
 ###############################
 
-AM_LDFLAGS += $(P2TC_LDLAGS)
+AM_LDFLAGS += $(P2TC_LDLAGS) $(P2TC_LIBS)
 AM_CFLAGS += $(P2TC_CFLAGS) -I$(top_srcdir)/seamless-clone
 
 LIBS = $(op_libs)