gallium/tests: conditionally include sw/dri winsys

In all fairness we allow the gallium tests to be build with --disable-dri
which will result in the approapriate winsys to not be build, thus the
build will fail.

  ./configure --disable-dri --with-gallium-drivers=svga --enable-gallium-tests

Cc: Brian Paul <brianp@vmware.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>

src/gallium/tests/trivial/Makefile.am

@@ -13,11 +13,15 @@ AM_CPPFLAGS = \
 
 LDADD = $(GALLIUM_PIPE_LOADER_CLIENT_LIBS) \
 	$(top_builddir)/src/gallium/auxiliary/pipe-loader/libpipe_loader_client.la \
-	$(top_builddir)/src/gallium/winsys/sw/dri/libswdri.la \
 	$(top_builddir)/src/gallium/winsys/sw/null/libws_null.la \
 	$(top_builddir)/src/gallium/auxiliary/libgallium.la \
 	$(GALLIUM_COMMON_LIB_DEPS)
 
+if HAVE_DRI
+LDADD += \
+	$(top_builddir)/src/gallium/winsys/sw/dri/libswdri.la
+endif
+
 if NEED_WINSYS_XLIB
 LDADD += \
 	$(top_builddir)/src/gallium/winsys/sw/xlib/libws_xlib.la \