Created by: shawndenbow
This commit gets core DR building on MacOS 64-bit.
+ change error notifications to warning to allow build to continue
+ define SC_FIELD for 64-bit registers r8-r15 and update references
+ update dynamorio_mach_dep_syscall to use syscall for 64-bit
+ update dynamorio_mach_syscall to use syscall for 64-bit
+ change code referencing eflags to xflags for cross platform compat
+ misc code fix-ups