Missing typedef for OrcTargetPowerPCFlags

Currently, OrcTargetPowerPCFlags will end up in a library as a local symbol, which causes linking problems on some platforms (e.g. duplicate symbol error on Darwin/macOS).

I guess the definition lacks typedef, so here's my fix:

--- orc/orctarget.h.orig
+++ orc/orctarget.h
@@ -19,7 +19,7 @@ enum {
   ORC_TARGET_FAST_DENORMAL = (1<<31)
 };
 
-enum {
+typedef enum {
   ORC_TARGET_POWERPC_64BIT = (1<<0),
   ORC_TARGET_POWERPC_LE = (1<<1),
   ORC_TARGET_POWERPC_ALTIVEC = (1<<2),