[gimp] app: fix app/tests linking

[Ell <ell src gnome org>]

commit 7a02859d32c5c527e59a5cffad41309f7f1c228b
Author: Ell <ell_se yahoo com>
Date:   Sun Sep 2 04:55:40 2018 -0400

    app: fix app/tests linking
    
    Required since commit 80bf686c9447f59bdc72cc9adb018ef1a0d83444.

 app/tests/Makefile.am | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)
---
diff --git a/app/tests/Makefile.am b/app/tests/Makefile.am
index c611bd4722..55dd04c2c7 100644
--- a/app/tests/Makefile.am
+++ b/app/tests/Makefile.am
@@ -53,6 +53,10 @@ libgimpmodule = $(top_builddir)/libgimpmodule/libgimpmodule-$(GIMP_API_VERSION).
 libgimpwidgets = $(top_builddir)/libgimpwidgets/libgimpwidgets-$(GIMP_API_VERSION).la
 libgimpthumb = $(top_builddir)/libgimpthumb/libgimpthumb-$(GIMP_API_VERSION).la
 
+if PLATFORM_LINUX
+libdl = -ldl
+endif
+
 if OS_WIN32
 else
 libm = -lm
@@ -134,9 +138,11 @@ LDADD = \
        $(Z_LIBS)                                                       \
        $(JSON_C_LIBS)                                                  \
        $(LIBMYPAINT_LIBS)                                              \
+       $(LIBUNWIND_LIBS)                                               \
        $(INTLLIBS)                                                     \
        $(RT_LIBS)                                                      \
-       $(libm)
+       $(libm)                                                         \
+       $(libdl)
 
 gimpdir-output:
        mkdir -p gimpdir-output