Disable sphinx build if PNG support is disabled

Author: wasamasa

configure.ac

@@ -828,7 +828,7 @@ CAIRO_ENABLE(symbol_lookup, symbol-lookup, auto, [
 PKG_CHECK_MODULES(glib, glib-2.0, have_glib=yes, have_glib=no)
 AC_SUBST(glib_CFLAGS)
 AC_SUBST(glib_LIBS)
-AM_CONDITIONAL(BUILD_SPHINX, test "x$have_glib" = "xyes" -a "x$have_windows" = "xno")
+AM_CONDITIONAL(BUILD_SPHINX, test "x$have_glib" = "xyes" -a "x$have_windows" = "xno" -a "x$have_png" = "xyes")
 
 save_LIBS="$LIBS"
 AC_CHECK_LIB(rt, shm_open, shm_LIBS="-lrt")