disable Orc if CET is on

If we are building with -fcf-protection (run-time checking of
indirect jumps) then Orc won't work. Make sure it's off.

Orc may support -fcf-protection in the future, but does not in June 2019.

https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html#index-fcf-protection
https://gitlab.freedesktop.org/gstreamer/orc/issues/17

see https://github.com/libvips/libvips/issues/1006#issuecomment-501802550

ChangeLog

@@ -8,7 +8,8 @@
 magic number [przemyslawpluta]
 - much faster ismagick() [jcupitt]
 - better behaviour for vips_region_fetch() if request lies partly ouside image
-- remove band limits [erdmann]
+- remove 256 band limit in arithmetic.c [erdmann]
+- disable Orc if building with CET [lovell]
 
 21/9/18 started 8.8.0
 - much faster smartcrop [lovell]

libvips/include/vips/vector.h

@@ -34,6 +34,19 @@
 #ifndef VIPS_VECTOR_H
 #define VIPS_VECTOR_H
 
+/* If we are building with -fcf-protection (run-time checking of
+ * indirect jumps) then Orc won't work. Make sure it's off.
+ *
+ * Orc may support -fcf-protection in the future, but does not in June 2019.
+ *
+ * https://gcc.gnu.org/onlinedocs/gcc/\
+ * 	Instrumentation-Options.html#index-fcf-protection
+ * https://gitlab.freedesktop.org/gstreamer/orc/issues/17
+ */
+#ifdef __CET__
+#undef HAVE_ORC
+#endif
+
 #ifdef HAVE_ORC
 #include <orc/orc.h>
 #endif /*HAVE_ORC*/

libvips/iofuncs/vector.c

@@ -71,11 +71,13 @@ gboolean vips__vector_enabled = TRUE;
 void
 vips_vector_error( VipsVector *vector )
 {
+#ifdef HAVE_ORC
 #ifdef HAVE_ORC_PROGRAM_GET_ERROR
 	if( vector->program )
 		g_warning( "orc error: %s", 
 			orc_program_get_error( vector->program ) ); 
 #endif /*HAVE_ORC_PROGRAM_GET_ERROR*/
+#endif /*HAVE_ORC*/
 }
 
 void 
@@ -102,6 +104,7 @@ vips_vector_init( void )
 	if( g_getenv( "VIPS_NOVECTOR" ) || 
 		g_getenv( "IM_NOVECTOR" ) ) 
 		vips__vector_enabled = FALSE;
+
 #endif /*HAVE_ORC*/
 }