build: Don't try to build weston-info if client build is disabled

The weston-info sources are defined conditionally in the if BUILD_CLIENTS
section, but we always added weston-info to bin_PROGRAMS.

https://bugs.freedesktop.org/show_bug.cgi?id=72812

clients/Makefile.am

@@ -1,6 +1,4 @@
-bin_PROGRAMS =					\
-	weston-info				\
-	$(terminal)
+bin_PROGRAMS = $(install_clients)
 
 demo_clients = \
 	$(clients_programs)			\
@@ -63,7 +61,7 @@ weston_simple_egl_LDADD = $(SIMPLE_EGL_CLIENT_LIBS) -lm
 endif
 
 if BUILD_CLIENTS
-terminal = weston-terminal
+install_clients = weston-terminal weston-info
 
 clients_programs =				\
 	weston-flower				\