[Support] Add storage specifier for MachO::NListType.

This should fix UB warnings from the sanitizer bots: LLD performs bit
manipulations on enums of this type, and these are UB if the underlying
storage type isn't specified.

llvm-svn: 277251

llvm/include/llvm/Support/MachO.h

@@ -302,7 +302,7 @@ namespace llvm {
       N_EXT  = 0x01
     };
 
-    enum NListType {
+    enum NListType : uint8_t {
       // Constants for the "n_type & N_TYPE" llvm::MachO::nlist and
       // llvm::MachO::nlist_64
       N_UNDF = 0x0u,