Build: Remove Gnulib dependency from tests.

The tests do not use any Gnulib replacements so they do not need to link
libgnu.a or have /lib in the include path.

tests/Makefile.am

@@ -26,15 +26,10 @@ EXTRA_DIST = \
 AM_CPPFLAGS = \
 	-I$(top_srcdir)/src/common \
 	-I$(top_srcdir)/src/liblzma/api \
-	-I$(top_srcdir)/src/liblzma \
-	-I$(top_builddir)/lib
+	-I$(top_srcdir)/src/liblzma
 
 LDADD = $(top_builddir)/src/liblzma/liblzma.la
 
-if COND_GNULIB
-LDADD += $(top_builddir)/lib/libgnu.a
-endif
-
 LDADD += $(LTLIBINTL)
 
 check_PROGRAMS = \