Turn hb-gobject, and introspection off by default

Also enable bootstrapping without them.
diff --git a/src/Makefile.am b/src/Makefile.am
index fb7caf3..684e415 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -371,13 +371,13 @@
 	HBHEADERS="$(HBHEADERS) $(HBNODISTHEADERS)" \
 	$(NULL)
 
+if HAVE_INTROSPECTION
+
 -include $(INTROSPECTION_MAKEFILE)
 INTROSPECTION_GIRS = harfbuzz-$(HB_VERSION_MAJOR).0.gir # What does the 0 mean anyway?!
 INTROSPECTION_SCANNER_ARGS = -I$(srcdir) -n hb --identifier-prefix=hb_ --warn-all
 INTROSPECTION_COMPILER_ARGS = --includedir=$(srcdir)
 
-if HAVE_INTROSPECTION
-
 harfbuzz-0.0.gir: libharfbuzz.la libharfbuzz-gobject.la
 harfbuzz_0_0_gir_INCLUDES = GObject-2.0
 harfbuzz_0_0_gir_CFLAGS = \
@@ -408,6 +408,7 @@
 typelib_DATA = $(INTROSPECTION_GIRS:.gir=.typelib)
 
 CLEANFILES += $(gir_DATA) $(typelib_DATA)
+
 endif
 
 -include $(top_srcdir)/git.mk