presence: Enable use of JSON instead of YAML

When `--enable-json` is given at configure time, JSON runtime
configuration is used otherwise the default is to use YAML build time
configuration.

Tested:
    JSON used at runtime when `--enable-json` given at configure time
    generated.hpp not created when using JSON
    generated.hpp created by default when using YAML at build time

Change-Id: Ief4392c3e61ebd15e7310ed37fb390bd59b72d69
Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
diff --git a/presence/Makefile.am b/presence/Makefile.am
index 528de54..a9e62d3 100644
--- a/presence/Makefile.am
+++ b/presence/Makefile.am
@@ -30,9 +30,11 @@
 	-flto \
 	$(STDPLUS_CFLAGS)
 
+if !WANT_JSON
 BUILT_SOURCES = generated.hpp
 TEMPLATES = \
 	templates/generated.mako.hpp
 
 generated.hpp: $(TEMPLATES) ${srcdir}/pfpgen.py $(PRESENCE_CONFIG)
 	$(AM_V_GEN)$(PFPGEN) > $(builddir)/$@
+endif