Make it possible to disable the fallback shaper at configure time

The OT shaper supersedes the fallback shaper in every case
and the latter become an extra weight for 99.9% of users.

configure.ac

@@ -127,6 +127,12 @@ if $have_ot; then
 fi
 AM_CONDITIONAL(HAVE_OT, $have_ot)
 
+have_fallback=true
+if $have_fallback; then
+	AC_DEFINE(HAVE_FALLBACK, 1, [Have simple TrueType Layout backend])
+fi
+AM_CONDITIONAL(HAVE_FALLBACK, $have_fallback)
+
 dnl ===========================================================================
 
 AC_ARG_WITH(glib,

src/Makefile.am

@@ -27,7 +27,6 @@ HBSOURCES =  \
 	hb-buffer.cc \
 	hb-cache-private.hh \
 	hb-common.cc \
-	hb-fallback-shape.cc \
 	hb-face-private.hh \
 	hb-face.cc \
 	hb-font-private.hh \
@@ -119,6 +118,10 @@ HBHEADERS += \
 	$(NULL)
 endif
 
+if HAVE_FALLBACK
+HBSOURCES += hb-fallback-shape.cc
+endif
+
 if HAVE_PTHREAD
 HBCFLAGS += $(PTHREAD_CFLAGS)
 HBLIBS   += $(PTHREAD_LIBS)

src/hb-shaper-list.hh

@@ -52,4 +52,6 @@ HB_SHAPER_IMPLEMENT (uniscribe)
 HB_SHAPER_IMPLEMENT (coretext)
 #endif
 
+#ifdef HAVE_FALLBACK
 HB_SHAPER_IMPLEMENT (fallback) /* <--- This should be last. */
+#endif