Fix mod-test build failure

Problem reported by Glenn Morris in:
https://lists.gnu.org/r/emacs-devel/2019-02/msg00739.html
* test/Makefile.in (HYBRID_MALLOC, LIBEGNU_ARCHIVE):
New macros, taken from ../src/Makefile.in.
(MODULE_CFLAGS): Add -I$(srcdir)/../lib.
($(test_module)): Link $(LIBEGNU_ARCHIVE) too.

test/Makefile.in

@@ -254,17 +254,21 @@ else
 FPIC_CFLAGS = -fPIC
 endif
 
+HYBRID_MALLOC = @HYBRID_MALLOC@
+LIBEGNU_ARCHIVE = ../lib/lib$(if $(HYBRID_MALLOC),e)gnu.a
+
 # Note: emacs-module.h is generated from emacs-module.h.in, hence we
 # look in ../src, not $(srcdir)/../src.
-MODULE_CFLAGS = -I../src $(FPIC_CFLAGS) $(PROFILING_CFLAGS) \
+MODULE_CFLAGS = -I../src -I$(srcdir)/../lib \
+  $(FPIC_CFLAGS) $(PROFILING_CFLAGS) \
   $(WARN_CFLAGS) $(WERROR_CFLAGS) $(CFLAGS)
 
 test_module = $(test_module_dir)/mod-test${SO}
 src/emacs-module-tests.log: $(test_module)
-$(test_module): $(test_module:${SO}=.c) ../src/emacs-module.h
+$(test_module): $(test_module:${SO}=.c) ../src/emacs-module.h $(LIBEGNU_ARCHIVE)
 	$(AM_V_at)${MKDIR_P} $(dir $@)
 	$(AM_V_CCLD)$(CC) -shared $(CPPFLAGS) $(MODULE_CFLAGS) $(LDFLAGS) \
-	  -o $@ $<
+	  -o $@ $< $(LIBEGNU_ARCHIVE)
 endif
 
 ## Check that there is no 'automated' subdirectory, which would