[gimp/gimp-2-10] tools: fix linking error.

[Jehan <jehanp src gnome org>]

commit 0865e9db1f27154816f5e01483a55fa6064fdbaa
Author: Jehan <jehan girinstud io>
Date:   Sun Aug 12 15:12:22 2018 +0200

    tools: fix linking error.
    
    Though no error was raised during a native build, a cross-build was
    choking on this missing link to libgimpbase and failing.
    The error returned by the linker though was a bit amiss.
    
    Fixes:
    > gimp-test-clipboard.o: In function `test_clipboard_copy_callback':
    > tools/gimp-test-clipboard.c:419: undefined reference to `g_file_get_contents'
    > collect2: error: ld returned 1 exit status

 tools/Makefile.am | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/tools/Makefile.am b/tools/Makefile.am
index 7f18f29a5b..84568cb535 100644
--- a/tools/Makefile.am
+++ b/tools/Makefile.am
@@ -35,7 +35,9 @@ gimptool_@GIMP_TOOL_VERSION@_LDADD = \
 
 gimp_test_clipboard_@GIMP_TOOL_VERSION@_SOURCES = gimp-test-clipboard.c
 
-gimp_test_clipboard_@GIMP_TOOL_VERSION@_LDADD = $(GTK_LIBS)
+gimp_test_clipboard_@GIMP_TOOL_VERSION@_LDADD = \
+       $(libgimpbase)  \
+       $(GTK_LIBS)
 
 
 kernelgen_SOURCES = kernelgen.c